I think what has happened here is actually a culmination of factors, some intentional others not, all conspiring to favour Bismarck

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I checked the scripts a couple of weeks ago when one of your videos started showing this trend, good news is nothing is outright broken
Running the numbers a bit more, the majority of this trend is due to all the towns the Colonel has occupied - each settlement is 2 FS/turn, each town is 5. Metz, Strasbourg and Belfort are actually 0. Given the amount of land the Colonel has occupied, it adds up to a fair bit - ballparking an estimate here it's probably -200 or so for the French, and +200 per turn for the Germans (that is, each French turn AND each German turn).
I checked the numbers against the SC2 version, the only difference I could see is that the FS value of settlements in that was 1 instead of 2, but there's only about a dozen of them in the occupied area so it's not going to make an appreciable difference (I may set it to zero in 1.07, haven't decided yet).
In 1.04, when you started this game, war weariness was +75/turn for France and -50/turn for Germany in October (+125 and -100 in November onwards), which will slow the trend down a bit but won't be enough to reverse it. I upped these to +100/150 and -100/150 for France and Germany in Oct/Nov+ respectively for 1.05. Additionally in 1.05 I increased the starting French FS to 120 (from 100k), which would equate to a French FS of about 62% were you playing on the new version, instead of 52%.
As for whether I should change something further, I'm not sure at this stage. The SC2 version has been out for ten years at this point, getting updates for a good part of that time, so one would think that any major balancing issues would have been resolved long ago - and this campaign is near enough a 1:1 copy of the old version (I did a parallel AI/AI test of both versions last year, the graphs at the end of the game were remarkably similar!). Additionally, I'd have a hard time calling this campaign a likely French victory based on the footage I've seen (I've watched all of both your and the Colonel's turns) - he controls all the objectives and looks to still have an upper hand units-wise. 1870/10/11 is turn 40/96, so you're 42% the way through the game, that being the case a "fair" FS figure for the French is 58% at that point (given the Germans lose if they don't control all the minor objectives by game end). Or at least, that's what the numbers say.
All told, I think I'd need to see more of this game before I can make a judgement on balance - I don't want to make it too hard for the Germans either, and except for the Thionville mess-up the Colonel hasn't made any really grave errors that I've noticed.
- BNC