Fortification Construction predictability

[Wiedrock]

Since tyronec brought up the destruction of Fortifications, I decided to re-visit my attempts to predict Fortification Constructions which I always had some some issues with. The things observed, may be me and/or the manual may be missing some rules regarding the Fortification Construction or have wrong values stated eventually.
Generally when now looking at the numbers it is hard to say that something is better/worse than expected, if I am not sure what the "baseline" is. So some statements may be wrong when referring to exceeding/subceeding expectations.

TLDR Questions:

1. Why is the Fort Construction sometimes much larger then expected? (no construction SUs are involved).
2. Where does the general deviation of percentages come from? (rolling the exact same turn multiple times)
3. Why does moving a HQ closer/further to/from CU cause a change in fort level progress? (there are no leader rolls, or are there?)
4. Are there any Leader rolls being performed to built Fortifications? (only looking at lvl 0→1 Fort building)
5. Why is the fort construction much slower in Swamp Hexes then 75% of another (non-Clear) Hex? (the manual states "reduced by .25").
6. Do Support Squads (in CUs/HQs) and/or the have/need-percentages of Support Squads have any impact on the fortification construction?
7. What MP/SMP are SUs using which were this turn attached to a CU/Fortified Zone? What if the HQ moved before attaching them?

Setup:
I have a testing setup Soviet side where I removed all construction SUs and there are no engineer SUs around. So those are out of the game. Additionally I am only looking at lvl 0→1 construction.

1.I have created a spreadsheet where I input SMP and Construction Value of a unit (besides terrain and weather).
This way I can somewhat predict the resulting Fort level increas (level 0→1), but I encountered some oddities. The biggest one being, that (assuming my forumla in itself is correct) you have many nice resulting percentages which match the ingame observed results, but then there are some which show a 10-60%'ish larger increase of Fort level then expected/calculated (so instead of bringing a Fort to 30% it may end up with 45%).
I can't see where in the manual this surplus in Fort Construction is comming from. So please tell me where to look at to figure that one out!

Further smaller oddities:

2.When rolling the same turn many times with multple Units being tracked regarding their advancement for constructing fortifiactions, the percentages you get are varying (~ +/- 5% points at least).
I don't see where this randomness is found in the manual and what is causing it in the first place.

3.The manual does not refer to leader rolls when it comes to Fortification Construction with the exception of mentioning a Admin roll when it comes to building Fortifications "greater than 3".

Admin Checks: Fortification build rates for building fortifications greater than 3 can be divided by 2 if a leader admin check fails.

Changing the Leaders seem to generally confirm, that there is no leader roll (I hope), but two contrary instances seem to (for whatever reason) lower the Fort Level built.
A: moving all HQs of the chain far into the east (far, far away).
B: move all HQs of the chain pretty close to the observed CUs.
In both cases I can see an decrease in Fort levels (not too big but observable). This testing increases the aforementioned ~+/- 5% to sometimes more than ~+/- 15%. I observed this several times, if the RNG tricked me it'd be rly bad luck. What may be causing this?
Using a edited Scenario with all Leaders having Rating 9 seems to show an effect (opposed to using normal leader changes - where the difference is not that big), but I won't bet on my observations.
4.Are any Leader rolls being performed?!?!

5.Swamp Hexes seem additionally odd.
The manual mentions:

Terrain: In a swamp hex, these values are reduced by .25 (and the maximum fortification level in a swamp hex is 3).

But it appears (applying the same formula and just changing the terrain modifier) it is not reduced by 0.25 (assuming it means x0.75(?)) but rather to x0.25 (eventually x0.33 - I can't say for sure).
So this section I am sure needs some Manual clarification.

6.
The Manual is somewhat confusing when it comes to Support Squads. Additionally from previous testing I have seen CUs with 1 Construction Value build a whole Fort level by themselves (no Construction/Engineer SUs present) on German side when HQs were not edited, this changed when TOEs of HQs were reduced to 5 Support Squads per HQ.
Therefore, do Support Squads (in CUs/HQs) and/or the have/need-percentages of Support Squads have any impact on the fortification construction?

EDIT:
added link to sheet
added Question 7.

[Joel Billings]

TLDR Questions:

1. Why is the Fort Construction sometimes much larger then expected? (no construction SUs are involved).
2. Where does the general deviation of percentages come from? (rolling the exact same turn multiple times)
3. Why does moving a HQ closer/further to/from CU cause a change in fort level progress? (there are no leader rolls, or are there?)
4. Are there any Leader rolls being performed to built Fortifications? (only looking at lvl 0→1 Fort building)
5. Why is the fort construction much slower in Swamp Hexes then 75% of another (non-Clear) Hex? (the manual states "reduced by .25").
6. Do Support Squads (in CUs/HQs) and/or the have/need-percentages of Support Squads have any impact on the fortification construction?
7. What MP/SMP are SUs using which were this turn attached to a CU/Fortified Zone? What if the HQ moved before attaching them?

Each (on map) combat unit that is attempting to dig in tries to find a construction unit to assist in the digging. It must pass a leader Admin check, but it can check multiple times if there are multiple SU units in qualifying HQs. Once it succeeds in getting help from a SU, it stops checking. So one CU will get at most one SU to assist. Once an SU assists one unit, it is unavailable to assist another unit. Units can check for SUs in HQs up to 3 levels of command up the chain, so Corps/Army/Army Group, or Corps/Army/HighCommand as examples. The range to the HQ in hexes must be within 5/Corps, 10/Army, 15/AG-Front, 20/HighCommand. A support unit that has just been reassigned to a HQ during the turn is not available to help, but the HQ moving has no impact on the SU inside the HQ (and the SU always assumes it has full MPs available for construction). SUs in an HQ adjacent to an enemy will not provide construction support. Swamp is a x.25 modifier (divide by 4). We think the system looks at the fort level you have when you start building to determine how much it will take to build each fort point. So if you are at fort level 0 (98%), you will build faster than a unit at fort level 1 (0%) (not ideal, it was a code simplification issue). Support level versus support need of a unit does impact a units construction ability (reduces it if short of needed support). Hopefully realizing all of the above, the system is working.

The one thing we aren't sure about is population help building forts. Pavel is going to take a look at this and see if it's working as intended. It seems to be very separate from the normal fort construction routines.

[Wiedrock]

Thanks for the answer, this explains all the SU stuff which is awesome since it is also of concern (altough I have them removed in my test).

5.

Swamp is a x.25 modifier (divide by 4).

This would need to have the "reduced by .25" of the manual needed to be changed "reduced to .25" if my english doesn't fail me?!

6.

Support level versus support need of a unit does impact a units construction ability (reduces it if short of needed support).

This was something I was somehow expecting, so more to look for/account for.
I guess I gotta rerun all tests to include this metric which may explain some of the oddities.

[Joel Billings]

Finally closed the loop as Pavel looked into City population aid to fort building. We can confirm it's working, and appears to be working as documented.