ORIGINAL: bevilacqua
Thanks for taking your time and doing some tests. But, yet I find it strange since my supply points were to the rear. What do the units use: they retreat in the direction of the supply point, no matter the terrain between them or they try to find the shortest path, in which case they would avoid the hills behind and go for the road on the right side? The stack on this road is the only one, in addition to the one just above the broken units, which may have attained the stacking limit. I think that using the direction or stablishing a safest path would be the best solution, but I really don't know what the game uses.
What scenario were you playing, and where on it was the combat?
I know that using overruns make it easier, but that would force units to ignore the nice path in front of them and go after the enemy. Suppose I placed the trucks on swamp hexes along improved road ones, just to deny this nice advancing path to my enemy. Or, what's worse, place them on dunes (not trucks). The fact is that, if you have units all around and want to use a straight path ignoring them, you'll have to pay the move cost, even if they are tiny (relatively). Obviously, I went to an extreme case. In most cases units won't be so tiny and won't even be dislodged. In those cases I think they should pose some restriction to movement, but proportional to their size and even lower if they are tiny and the enemy is able to spot their size.
Clearly it can be an irritant in many cases. But, baring the bizarre examples you conjured up, it, in general, is not the reason breakthroughs are so hard.
I know it would break some scenarios, but that could be offered as an advanced rule. I mean, some scenarios would even benefit from it and the notion of breaking scenarios is also arguable if we consider that a lot of scenarios are not even balanced. I think that the better way to balance a scenario is playing it once and stablishing your victory conditions from this first time. Most of the time, the victory conditions stablished by the designers are unbalanced, because of bad design or even, perhaps, because of changes in the game along those years, which isn't all that bad (I think that most players don't want to go back to the earlier versions) and one can always stablish personal victory conditions.
It's in the Wishlist already: item 7.7.