Found it in an older mod !:
LAST_PLANE_DIE_FACTOR = 0.5, -- chance to kill last plane if our damage was too low to kill even one plane (1 = 50% chance if it had 50% dmg)
That used to be a define.
Some other defines changed as well, not sure what effect they'd be having.
These are the current ones:
AIR_COMBAT_FINAL_DAMAGE_SCALE = 0.015, -- % how many max disrupted only planes are alloed to die in a single combat
AIR_COMBAT_FINAL_DAMAGE_PLANES = 50, -- scaling/control for when only very few planes exist to stop roundoff issues
AIR_COMBAT_FINAL_DAMAGE_PLANES_FACTOR = 0.1,
whereas before, there was only this:
AIR_COMBAT_FINAL_DAMAGE_SCALE = 0.5, -- % how many max disrupted only planes are alloed to die in a single combat
So...