Movie Render pipeline (preview) window size/resolution

Hello, i have a quick question regarding setting the size/resolution for the new window that appears after i hit ‘Render (Local)’ button in MRQ.

I want to set it to certain resolution since i need to get specific coordinates of an object based on the resolution itself. It defaults to 1280x720.

I tried setting the ‘new window resolution’ option in editor preferences but nothing changes.
Also the console command ‘r.SetRes’ doesn’t work for me for some reason…