We strongly recommend to test the emulator in standalone mode before adding it to mGalaxy.
Have you tried to run KegaFusion standalone and then switch to full-screen?
I've done the test...and I get a "Unable to set Display Mode" error (Windows 8.1, 1920*1080, nVidia)
Fortunately, this can be fixed by running it in compatability mode for windows 7:
Right-click on "Fusion.exe" application > Properties > 'Compatibility' tab > Check 'Run this program in compatibility mode for' Windows 7
(While you're there, you could test with 'Disable display scaling on high DPI settings' too)
To end, I would add that you'd better try setting full-screen in the settings below 1080! Not really sure but i think Fusion has problems running full-screen at 1080!