Looking at the Delphi source code fsStayOnTop is slightly different (two more flags in last param)
SetWindowPos(Handle, HWND_STYLE[FFormStyle = fsStayOnTop], 0, 0, 0, 0, SWP_NOMOVE or SWP_NOSIZE or SWP_NOACTIVATE or SWP_NOOWNERZORDER);
HWND_STYLE[FFormStyle = fsStayOnTop] is equal to HWND_TOPMOST if fsStayOnTop otherwise HWND_NOTOPMOST