If you are using fiber paper, isnt glass needed to kept it flat?
If the paper curls, the negative will be much more than .5mm away from the paper. There is also a higher probability that the negative will shift, especially if you are waving your hands above it to dodge or burn.
You also mention the circles of confusion will be "10 times smaller than they need to be for most "8x10 at 'normal' viewing distance"" Isnt the entire point of making 8x10 contact prints to have the sharpest and most tonally beautiful print possible, not merely sufficient for a certain viewing distance? After all, when i view prints in a gallery i like to get as close as possible and study every detail, especially with a smaller print.