Ashe's Q needs a stacking mechanic

Or drastically decreased mana cost when attacking already slowed targets.

Currently, Ashe's Frost Shot will consume 8 mana per attack, meaning that the higher your Attack Speed is, the more mana you burn. On top of this however, it doesn't have any form of a stacking mechanic. What this essentially means is that, as your Attack Speed rises, you are paying more mana for the exact same effects.

I realize from a balance perspective it probably doesn't make too much of a difference, but I still think that it's just plain odd and clunky. Pay more and gaining no benefits for it just because I'm getting more Attack Speed, a stat I'm certain to build as an ADC? Ehh...

EDIT: So the second paragraph apparently didn't do a good job explaining what I'm trying to say.

I just thought it was a weird gimmick Ashe has to put up with. Hence why I said:

I realize from a balance perspective it probably doesn't make too much of a difference

That in mind, I don't need the advice to turn Ashe's Q off between Q proc'ing autos. I just thought it was something funny to point out. ('- 3 -)