Well, to get a response, the first thing one must do is way more than complain that the game is not working correct because of a few events within you game that does not seem to be working to your wants.
It takes seeing a problem, testing it out to see what the game is actually doing to verify what the results are within the game as to the item in question and then to be able to back that up with hard facts as to why it is incorrect.
So first thing to note here, moving units through woods or wheat fields with the enemy waiting in a defensive position is normally going to get you slaughtered in the game, it has been that way from the early releases of cm2. So not sure why you think its a new issue now. Unless you have not played with the later periods much. Things that are one sided in the WW2 titles are just that much worst in the later periods because of the firepower involved.
There is no smart way to move up on a enemy unit other than when you have firepower on them and they are pinned or moving when you are providing concealment so they cannot fire on you. Other than that, you are asking to get your ass kicked.
Now as to 40 men moving through wheat and taking on ten men in wait.
It sounds like you assume the 40 should have the advantage, that once the firing starts, they should be able to spot that fire and return with heaver amounts of fire and win the engagement.
Well lets play this out in RL thinking.
First, the 10 will spot and engage almost every time first, in RL and within the game.
Second, they will open up on targets they see, the enemy will likely have no targets.
Third, some of the approaching enemy should and will die at the distances you are discussing
Forth, if you are being shot at and some of your men go down, most likely you are all hitting the ground and looking for cover if any is possible. Not looking to fire back at a unclear target.
Once laying down in wheat field or woods, pretty hard to see very far. thus still not seeing the enemy.
Plus out of the 40 men, in all truth only a handful will likely be in position to see the enemy even if they were willing to try and return fire.
So with my version of the fire fight, it sounds like the game is getting it about correct. So lets discuss how it should be if I am missing something here.