LSB (left sidebar) can be pinned or made flowing over.
RSB (right sidebar) is unique for FCHD panels. It's stationary - you cannot resize it or change its position.
Let the RSB properties be changed. Let it be horizontally resizable first, and then flowable too. So all apps opened in its panel would be adapted to their best size. Let the right slide line of main page panel (left for FCHD panels) be movable horizontally (left/right), whether flowed ot pinned.
I'm not "all or nothing" guy. I'd appreciate setting size of the panels, at least. Let it be - one size for all, but a property I'd be able to set to my own needs.