Focus height makes a big difference for thicker materials. You can’t just keep slowing it down or repeating the cut, but there’s also no general recommendation - you need to test for your material to get desired results. Pine is going to be a bear because it has so much resin content.
Each of these pairs of cuts (end view of 3/8" maple which is actually .39") are at the same speed, but the right cut is focused on the surface, the left (deeper) one is focused at 1/2 that height:
