
Re: fit headless DP on a Mac Mini
The setup involves several components, the graphics hardware, OS driver, monitor and fit-Headless itself.
Fit-Headless contains EDID EEPROM that is programmed with a list of supported resolutions (
http://fit-pc.com/wiki/index.php/FAQ:fit-Headless), and just emulates the display enabling the target PC to output the content with its native resolution.
I think the root cause of your case lies somewhere in graphics hardware or the driver.