How to change the scroll distance of page up and page down buttons?

I would like to change the amount/distance that a window or page scrolls up/down when using the page up/down keyboard buttons. I think it's poor design that the default behavior scrolls exactly 100% of the visible window... it keeps things near the top and bottom edges of the screen stuck in uncomfortable reading positions; scrolling 50% of the page would be much more flexible by allowing you to reposition the window contents towards the middle.

It's a nuisance to use the mouse scroll wheel, especially now that I'm trying to use voice commands to avoid the mouse entirely.