Héli spawnkilled / useless heliport's flak /

Heli are pinata for anything that rolls or flies, héliport’ flak is completely incapable of hit anything at any distance, planes and even enemy heli spawnkill in complete tranquility !
Give the heliport a credible flak : <1km=100% hit / <2km=50%hit / <3km= 20%hit
as well as invulnerability when placed on the ground on the heliport !