One question ice nova of frostbolts

I supported frostbolt with Greater projectiles and greater volley. 9 projectiles total.

Any disvantage? People only use greater projectile and returning projectiles. More projectiles better, right?

you only need 4 projectiles to get full overlaps on ice nova of frostbolts, more projectiles per cast just eats up support gem slots that could better be spent on other things.

Thank you for the answer. After a lot of time I read the full gem description. Yes. Max 4 frostbolts, XD