Going through the rules of DBA 2.2, I pondered some of the strangeness of the combat modifiers, trying to reconcile them in my mind. Here are some thoughts on what works and what is completely strange.
In melee double pikes get +3 and double warbands +1 vs all but cavalry, psiloi, light horse, scythed chariots and bows. This is because these attackers all have some sort of missile weapons or are designed to crash through the ranks (scythed chariot) so the second rank could not actively help the front. That actually makes sense.
Double spears get +1 when fighting knights or other spears. OK. Huh? This makes no sense. If you are going to allow spears to support other spears, then one would think they would perform similarly to pikes with a +1 instead of a +3. Not quite sure why the difference.
Psiloi supporting blades spear and auxilia confer a +1 bonus when attacking mounted, or forts or camps. This is because 1) the target is vulnerable to missile fire or 2) the shooting overhead is making the defenders of the fort/camp keep their heads down. This makes sense.
All of the tactical factors seem pretty straight forward. As a whole, I think the support relationships are pretty well thought out save the Spear. in the next iteration, I would love to see that standardized to behave like pikes do now. Will it happen? That remains to be seen.