Fix separator height calculation
Fix separator height calculation

Fixes #1796

Also rearranged this code to more closely mirror the similar code above
so future discrepancies are easier to spot.

ascent12/sway,taiyu-len/sway,1ace/sway,taiyu-len/sway,1ace/sway,ascent12/sway,taiyu-len/sway,1ace/sway,SirCmpwn/sway,ascent12/sway