is there any “simple” way (i.e. parameter or flag) of causing the vertical
page scroll to be slightly less than a page/viewport size. The default
appears to be the full viewport size, which is of course not wrong, but can
result in half a line at the bottom becoming half a line at the top so a
second increment is required to get it into view. Something like a 90% of a
page scroll would solve that.

I have no doubt it can be done “manually” via call backs but is there a
parameter that sets the size (so I can continue being lazy).