So far everything checks out ok, so I'm not sure where the frustration is coming from, especially since I always warn against them unless you're up against no hope to win

Let's look at what's happened in our VERY SIMPLE TO UNDERSTAND EXPERIMENT:

I used the scenario designer to set up some trials. The axis tanks have a 70% quality rating. During the MOVEMENT PHASE, I chose both of these armoured units to switch to withdraw. Their default defense rating was 20, but we can see they auto-changed immediately to 25 because units in withdraw do get a little bit of a defensive bonus, which helps to counter their very risky maneuvers.
Due to an avoidance of (bad luck), and good quality, our rolls (including the -10) modifiers have put both units under our quality rating value of 70 (100 sided die cast). So we successfully pass our W/D checks and are able to leave E-ZoC, as can be clearly seen.
It seems to be working as intended...