Repro:
* Right click in shelf, position shelf on right
* Right click in shelf

Menu is now mostly offscreen, so you can't select the shelf position.

I think the problem is that the workspace bounds used to place the menu onscreen are different than the X window bounds. It might be something like the workspace defaulting to 1366 pixels wide vs. the X window being hardcoded to 1024.

I'm not sure where these values come from, but components/mus/ws/platform_screen_impl.cc and/or platform_screen_impl_ozone.cc might be related. Ditto ash/display/display_info.cc