Cya Oswald M8 (guess you are HM),

What I do is this:

I put on the field the infantry (as example) in place, each unit one by one.
For example I put a anticav unit at left, dragging it to have exactly the formation/lines I want, then I put the other units doing the same in the position I want. At the end I select all of them (with CNTRL button pushed) and then press G to make a group.
Doing this I have a group of Infantry in the desired order, and with the desired depth of anyone. From now on, any time you try to position/move the group on the Battlefield, they will keep the same order and depth, anticav will always stay on the left...
The only problem is that at end of battle, your units have many losses, and in this way they will keep always the same position/depth, resulting in a big distance between them (if for example I have 10 units left on one and 7 on another). The easy workaround is to select the group, press G to dismount it, then redrag the units on battlefield (at this point you will have all your previous group selected) and then press G again, to have a reasonable group for the end of the battle.

XXI_RAPAX_Brutus