Sounds like Arrow rain,
iirc its just based off atk, and no it will not apply fixed melee+ (but melee+ to elements will work) , however Dorry is still a good xtal
I assume you're an auto-attack sniper, you could go with 1 sec spam but the aspd would make it hard, I'd rather stick to fixed melee gear and fire AR whenever you please.
afaik for a vast majority of the skills I have heard of and seen, fixed melee does not apply to them