Perhaps a take away is not to keep EXTRASEAT empty if not a POS but rather state that you are purchasing the seat for an important personal possession, then stick something of reasonable size on the seat when seated.
If traveling with a child, I might consider putting a car seat in the window, but leaving it empty and letting the kid sit in the middle during boarding.
No idea if this would help. But, taking an analogous situation, certainly the GA would not have offloaded a seated cello (with its own ticket) without the cello's owner?