Re. pane size, it's normal tiling behavior. Panes can be take the full screen or some percentage (I like 1/2, 2/3, and 1/3). If the widths add to 1, both panes fill the screen.

If the widths don't add to 1, there are two possible behaviors (configurable). Either the newly focused pane adheres to the size of the screen (e.g., scroll right from the full screen editor and the half-screen browser is on the right border with half the editor visible), or the newly focused pane centers on the screen. I prefer the first behavior, but I make significant use of the "center pane" keybinding.

The Video Demo section in the README gives a pretty good demonstration of this behavior in the first 10-15 seconds.

Edit: To add to this thought and address some comments elsewhere about losing windows, I use "struts", which show P pixels of the panes to the left and right (when they exist) of the current view as a visual aid/reminder of where I am in the ribbon. These reduce the size of the tiled section of the screen and the calculation of pane size accordingly.