I had tried that before and just tried now. After trying for a few times, I figured that it doesn't really work.
The vertical divider will push the collection pane to the left for a while, and then collapse. If you then try to restore the collection pane size, you have to (1) pick the right divider, and (2) absolutely not drag it "the other way". Otherwise the middle pane opens again.
So any adjustment to panes would likely throw the middle open again. Not really a solution.