[Humakty]

What seems sure to me is that it is hard to combine chaff and regular units, because of the % of lose before a general rout check for all the army.
I generally use them separatelly. (I only field chaff in supplement of 3 or 4 battle mages, late game)
The main use I see for chaff early is to occupy your frontier forts or accelerate a siege. With 1 or 2 luck, you usually have enougth chaff for free, so you don't have to build any.
This advice is based on my experience and style of gameplay, I do mostly play factions with heavy inf, and I dunnot know what to do with bandar and other factions like them.
As for the deployment, I put shields in the middle, with damage dealers on the flanks, sufficently backward so that my shields make contact first (and draw fire)