Undistorted view of flat image on the rift

I wanted to implement a curved screen mode in Virtual Desktop (viewtopic.php?f=29&t=8182) so the approach I took was to essentially render the desktop without distortion so that the pixels map 1:1 with the screen on the rift. If I used the default FOV, my eyes were not able to "converge" on the image. After a bit of trial and error I found that reducing the ICD (hopefully I'm using the right term) in half allowed me to correctly see the image without convergence problems. I essentially reduced the LeftTan and RightTan difference between the FovPort of the left and right eye. This somehow gave me a perfect angle when I looked at the image in the rift.

I wanted to ask if there was a more scientific reason as to why I had to do this? Will this work with different IPDs and perhaps different Interaxial Distances in future HMDs?

Thanks!