I assume you are playing some mod that is using the pex engine.
The real fix is to adjust the object attributes. There is now a differance between a tree,stone and tree,soft object (there are multiple physics modeling possabilities). Unfortunatly, the modders of the mod most want to play seem to expect me to make all the changes for them an that will never happen.
pex takes into account the mass and speed of your vehicle when you collide with an object. PE did not, so the modders used very strong attributes for every thing. The smallest tree is the next to strongest object in Ostpak for PESE. When playing Bob's pe3, try hitting the smallest tree at 10 KPH vs full speed in a TigerI. The speed vs mass fromula is one I am still willing to work on, same goes for the drift of the shell.
The pex 16.5 beta was released to show the modders how we had change the logic and physics engine from PE 1.2. Unfortunatly the only thing some modders cared to notice was how we broke the gameplay flow of PE.
pex was never ready for release as more then a beta for modders. The last publicly released version of the engine, 16.10e, addressed almost all playability issues not associated with the need to change object attributes needed for physics and AI pathfinding. You can find that by applying the last Goptics4 mod over Bob's pe3 (the file dll properties show version 16.10f).

there is a lot more to vent, but you don't want to hear it.
Back to your question!!!
In AISettings.ini is the entry Platooncollision=1 will prevent AI platoons from moving through lower numbered platoons during most move orders. Helpfull in properly scripting an advance. brings movement to a halt when the superior platoon become stuck.
UnitCollision=0 means the AI will move through another unit and ignore unit/unit collision.
Those are the ones you think you remember as ini entries.
Object collision is hard coded into the engine as a ratio of /unitdata/HitTable.csv entries. If your playing the 16.5 mod I am happy to discuss and change things if we agree it is more realisitic. The unreleased, current version even compares tree impact for height of impact vs AP and HE round. If your talking about pe3, good luck. I will not make for them, I will only help them understand how the data is used by PE, PESE, PEX.