[Zubersoft]

If you are using the vertical scrolling display mode, if the full page is visible, then tapping the sides of the screen will flip an entire page. If you use the tablet in landscape orientation or you increase the size of the page to be larger than the screen, then each tap will progress 33% of the screen height. If you need to be able to scroll portions of the screen at a time, the only way to effectively do that is with a bluetooth pedal. You can assign the pedal to scroll a certain percentage of the page or screen with each press in the pedal settings. You could also use the automatic scrolling feature to scroll your pages for you. If necessary, I'm willing to consider adding support for touch actions to scroll a percentage of the page or screen as well so you could just tap the bottom left/right corners, for example. 

Mike