Its a bit hit and miss Im afraid.
The output of the minireg on the speed does depend on its input.
So for a given input pressure, the reg has a certain maximum and minimum output pressure.
Depending on how the gun is setup you may be able to get the velocity low enough using a HP preset, but you will be running the minireg at the extreme end of its adjustment.
One thing to consider is upgrading the minireg instead of changing the air system. A better design of reg may give you a performance benefit as well as allowing a wider range of velocity adjustment.