I didn't notice this detail before, the aspect ratio probably shouldn't be 1; but setting the "3d_window_size" to 1 seems to have helped cylonsurfer.
@cylonsurfer: Yes, I'm using the latest OpenVR -- from Jan 2020, if I remember correctly.
I've been thinking about this problem and there's probably one other place where the scale can be applied: after the 2D projection. Scaling at any point before that is equivalent to what you guys already tested. So, I added a new parameter in this preview, called "post_projection_size":
https://www.dropbox.com/s/0zlmzd0lp7cbz ... 2.zip?dl=0
In this preview, the keys are the same; but the scaling shortcut (Ctrl + Up/Down) will change the "post_projection_size" instead of the 3d size. Honestly, I don't think it'll help and it may even cause blurry vision or double images. If so, please don't try to fix the blurry image, just set "post_projection_size" back to 1.
I'm starting to believe that this is the wrong question to ask. There's always some distortion when projecting 3D to 2D near the edges of the screen -- even without VR. This is something intrinsic to the way pinhole cameras work; but why is it bothering you so much? From the video posted above, the distortion *on the screen* doesn't look that bad. Maybe SteamVR isn't applying the right lens correction?