can't setGeometry a qwindow out of screen

I use qt5.9.6 on ubuntu 18.08 LTS, there is some problem I meet:

I try to use one qwindow to control another window's move, but when I try to setGeometry on another window with an out of screen position, it would be move to the edge of screen.

then I try to fix it, there are another problem:

set the bypasswindowmanagehint flag on the window whitch I want to control, but it would be a popup window, it would overlap all other window but I don't want this.

please help me with that, thanks.