MIxer window Default and resizing

When I work on a project I like to have the full mixer window open. When I close the project and re-open the default is a thin vertical strip which I have to resize. Ive tried "continue last session" in preferences and saving with the resized widow...but each time I re-open it defaults each time to the thin strip for the mixer window.

I also use an Elgato Stream Deck for Shortcuts and the toggle "show/hide mixer" (f10) but each time I hide the mixer and then show again, it goes back to the thin strip default setting ...so I have to re-size each and every time. Is there something I can do about that to change the default settings of the mixer window?
Thanks in advance!