why not frostbolt expand?

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Frostbolt: The player may cast Frostbolt and subsequently cast Ice Nova from the Frostbolt projectiles. If Ice Nova is cast this way, it will have 20% less area of effect and it may cast on up to 2 Frostbolt projectiles. If Ice Nova would normally repeat (ie. if it was supported by Spell Echo Support and/or Greater Spell Echo Support) and is cast on Frostbolt projectiles, it will expand again from those projectiles after a short delay. This does not cause the player to repeat the casting animation.

Frostbolt and triggers: If the player has any active Frostbolt projectiles and Ice Nova is triggered by an effect (such as Cast On Critical Strike Support), Ice Nova will automatically be cast on the Frostbolt projectiles.