There is the "Page Up/Down overlap" setting on the General page. Perhaps it would be easier said if it told how much of the area is scrolled, instead. For example, 100% for no overlap and 50% for 50% overlap. Reproducible: Didn't try
To be honest i think it's such and advanced/niche feature that ther is no short line to describe it correctly and that our current tooltip is good enough to describe what it does. Moreover we are already in "string freeze" stage for KDE SC 4.9 release meaning we'd need a really good reason to change the text. Do you know if there is any other viewer that implement this option and what text do they use? I tried looking at Adobe Reader and did not find anything.
After speaking with some people some of them think it's better the current way and some of them think it's better the way you suggest, hence it's a stalemate and can't change it since pleasing one half will unplease the other half. I'm marking this as wontfix as the tooltip and the handbook explanation should be enough to make you understand what it means. Thanks for caring about okular and reporting the issue :-)