Plus ofc, you will still see foot soldiers thrown into the air by cavalry, even by lighter units such as Cossacks. The formation changes I think are a result of the terrain, though I may be wrong. I noticed when I was play testing my historical battle that drag and drop of army formation turned up some weird changes but when the army reached its destination it reformed to original deployment. Also another drag and drop to another destination saw the original deployment pattern. M2TW has 'no go' and 'with difficulty' areas on the battle maps

.....Orda