Yamaha DTXpress/DTXplorer/DTXtreme

On the Rolands, I can loosely hold the drumstick, let it fall and hit 
the pad, and until the stick quits bouncing---the roland brain will 
register and output every single bounce. On the Yamahas in the 
stores i have tried this on, the yamaha system picked up the first 
three or four bounces and the last 5 or 6 (very light and quiet) 
bounces did not register. How can the Yamaha set be adjusted to pick 
up these sensitive rolls, if at all?????????????

Thank you