Audiofront

If you increase the "Travel" setting on the pedal adjustment page, the chicks and splashes from your hihat will become louder.
I tested this on a VH-10; 70 to 75 does the trick for me.

Related: if you get an open pedal stick hit when you do a heel splash, go to "Calibrate" and manually extend the right side of the green range indicator so that the fully open value for your hihat (i.e. foot off) is around 16.

Update: this no longer applies to the 1.3 (beta) version. There's a new Gain knob that lets you effectively dial in the velocity of hihat chicks and splashes.