You need to link your bullet speed value to your bluepowerbar.Height or to the power variable but thats an extra action which may not be needed
of course you can make it variable by adding a 'scale factor' according to the Height distance moved...
so what I mean is....1 x 2 x 3 x 4 x power scaling....etc etc
it could be ramped how ever you like ..easy gentle ramps or steadily increasing ..or power ramping
its up to you
does that make sense to you?