First of all, sorry for not responding...
Second of all, sorry for the HUGE pictures!
This is the best example I can offer, two eve-online installations, both windowed (two in fullscreen will never happen). You can't position them perfectly to look fullscreen.
This is just opening and positioning them a little:
Tick the boxes and this happens:
Perfect placement!
That is the best way of showing you. It also works on just one monitor to have a pseudo fullscreen as well. It works with
any program you can think of, fullscreened notepad as well.