I found this interesting treaty studying what are the parameters that influence a battle.
Here we mention the effects of rotation, the number of ranks and morale.
says that many ranks are not better than a few (see Cannae).
Also said that veterans and bravest are back in the ranks because they know better to resist anxiety.


http://utenti.lycos.it/campagneparal...sur-combat.pdf

(this is an italian version)

The pages of interest are: p. 9, 10, 11 but there is also many interesting parts.

Unfortunately i think M2TW engine can only do formations static and fixed property (such as Greek or barbarian) when the second rank begin battle only when the first rank are died or completely exaust.