I put a setting into MyLeoSettings, thanks to Chris George:
@string central-dock-widget = body
This lets me move panels around into three columns:
1. Left-hand column: the outline pane and below it, the Tabs pane.
2. Center column - the body pane.
3. Right-hand column (may not be shown) - for Viewrendered and other auxilliary displays.
I've used this layout for years. I like it because I want the maximum height possible for the body editor. The outline is more compact, so it doesn't need as much space. The Tabs pane also hardly ever needs to be full height. And more columns would make the others too skinny, especially the body pane.
I dislike intensely the default panel arrangement you get with Leo since it went to the new QT system in 6.0. In fact, I probably would have stopped using Leo if I hadn't learned from Chis George how to get around it.