Tried this out. I usually turn the page with the thumb of my gripping hand*
If my thumb lands half on and half off of the screen, it doesn't turn the page. If my thumb is fully on the screen, it will turn the page most of the time. If my thumb is inboard of the edge, say by 2cm, then it will almost always turn the page. I think this is actually Kobo's palm rejection at work.
* the hand I am using to grip the device, not my third, Motie hand
