@beelee If you only want AA rolls for the unit when attacking not defending then you need to set attackAA to 0 as it defaults to 1. Then set offensiveAttackAA to something greater than 0.
Uh, I don't think there is any limit on max dice sides but you might want to try it with something smaller first.
So your highlighted support attachment looks valid. It would make it so cruisers when on defense give -1 offensiveAttackAA to 99 enemy tact bombers and fighters.