Im using the same monitor as you and im having the same issue as you juat wondering if you figured out a solution?
This is my monitor
I have been trying to connect my Xbox One to it - but since the monitor only has 1 DP port and the xbox has a HDMI port, I had to get an active HDMI to DP adapter:
After connecting the Xbox and monitor with the adapter and using the adapter's usb cord to power it, the Xbox was only outputting a 640 x 480 resolution, occupying around one twelfth of the screen.
First I tried changing the resolution in the xbox settings - to 1080p or 720p - but changing the resolution made a message pop up on the monitor saying OUT OF RANGE.
I tried using a different DP cable, power cyclling the xbox and the monitor, messing around in the monitor's settings,. but nothing changed.
I need help in making the Xbox output a 1080p image.
Any help is appreciated.