We used to have an undistorted preview window with the console command
hmd mirror mode 2
but now it is still distorted in 4.11, did something change? Is there another method to get that undistorted preview window?
What about fullscreen window preview similar to how Unity demos show vr content?
I think it still works and what you are seeing is the hidden area mesh. Try turning it of with vr.hiddenareamask 0.
See this is why you’re amazing 
It’s hard work being this awsome all the time I can tell you!
But seriously maybe Epic would consider adding the option to only render the mesh to the right eye for such a use case?
That way you would still be saving some pixels.
Or go the unity approach and zoom in on the pixels crop to a 1920:1080 format and go fullscreen. The hiddenareamask would be cropped away for the preview anyway due to format.
It would be great with two options I think.
One square’ish aspect ratio using the full render from one eye. (black on the sides for 16:9 windows)
And one 16:9 extracted from the centre of the height. (throwing away pixels rows from top and bottom)
So they basically cut out a rectangle from the center of the heden area mask?
Yeah that’s my thought, you’d have a lower FOV being shown on screen, but it would use all of the screen real estate.