Please add to Track > Track layout > Mixer Panel menu next choice - "Session Mixer small fader" and please add function "Save height of Mixer Panel" - it is not fixing now.
For the existing themes users can and have to make their own new layouts (as well as themes) as they want them. Maybe you can present your layout idea in the theme forum and somebody can help you there?
As for the mixer panel height, you can save it as a screenset and call that. View/Screensets Layouts (Ctrl+E), Windows tab.
Mixer Panel add choice to layout
Linear Mode
