NPC Armies can use unlimited heavies

[NECROSTRATUM]

no longer needed

[Ogresalad]

NPC Armies should be bound by the same cohesion rules as you are. By "heavy" units are you referring to units like Aggressors or Inceptors? They have a cohesion limit of 6, due to the fact that Aggressors or Inceptors are easier to kill than something like an Annihilation Barge or Skorpekh Destroyers. Cohesion limits generally track alongside how difficult something is to kill - compared to Skorpekhs, Agressors/Inceptors respectively have 1 armor more or the same armor level, about 2/3rds of the health pool, with no health regeneration or Reanimation Protocol. In a toe-to-toe fight, Skorpekhs win every time.

But if you're referring to heavier units like Assault Terminators, Sanguinary Guard/Priests, Techmarines, Baal Predators, Land Speeder Tornadoes, etc., then those all have a Cohesion Limit of three. If you saw four or more of any of those with the cohesive armies box checked, then yeah something was wrong.

[NECROSTRATUM]

Yeah that is what I meant. I saw 4x BP's and 4x Aggressors and 4x Sg's