this rule never made sense to me and always thought it was a terrible rule (suppression for AA should only count against units with actual AA attacks)...so if everyone counts for suppression why doesnt every stand (that isnt a specialized AA unit) then get a single 6+ shot for example...cause to say everyone in weapons range counts for suppression means everyone should be able to shoot at the aircraft...conversely, if an aircraft wouldnt consider the non-AA units a threat because they cant actually damage it, why should the suppression count for the non-AA units...
love to have this explained in a way that makes sense...otherwise its actually too easy to negate the suppression for AA units because most ground units have longer ranged weapons than many of the guns on the aircraft in the game...
All true, but individual armies differ and the way they get to include AA in their lists vary, so I suppose they had to pick from one of three options:
1) Only AA weapons count towards the how many units in a formation are suppressed (which I think is what you're saying you'd prefer). This would however mean 1 Hydra in a formation with 10 Leman Russ would be useless when the formation has a single BM, and probably makes AA in mixed formations far too weak.
2) All units in the formation count towards the how many units in a formation are suppressed (which is the way the rules work). This is a pretty abstract way to do it, there's no real reason why a Hydra crew can manage to fire based on how many battle cannons can also see the target, but at least it's fairly consistent with the rest of the suppression rules.
Quite a few formations do suffer from the suppression rules (eg a formation with 3 Heavy AA Guns and 3 Trojans has its AA range drop from 60cm to 30cm if/when the heavy-bolter armed trojans have to count towards suppression).
3) AA Weapons can't be suppressed unless the formation is broken. This would allow the one Hydra in the formation to keep firing regardless of how many BM the formation takes, until broken. IMHO that makes as much sense as 2, but is probably over-generous to AA.
So with those 3 options for the rules, if 1 is too harsh and 3 is too kind, number 2 was probably the right choice.