On the Old MA system and a few of the newer armies, there were not any tried and true formulas. These are just bulit and playtested. With the new Rules release, there will be a Build Your Army section to use any miniatures. This should give you the formula for the AP.

I hope to have the BYA section ready for playtesting next month.

And Welcome!

Welcome aboard Dave,

There is no published formula for calculating the AP of a particular unit.  However, Rebel Minis is working on creating one.  I believe it will be included in the realease of the core rule book in March.  Please correct me if I am wrong, Mike.