I doubt seriously that the MainConcept encoder always assumes the input is 0-255 and therefore needs mapping to 16-235. Maybe the folks at MC were smart enough to actually include code to read the luminance values before mapping them.

If you feel like it, a good test would be to take a clip with luminance values in a smaller range than 16-235 and encode it in Pr or En. Then measure the resulting clip's luminance values on a scope. Does the luminance range expand to 16-235, does it stay the same, or does it get reduced by 16 in the shadows and by 20 in the highlights?

I'm not the one to do that test, since I've always been happy with the output black and white levels compared to the input black and white levels. (Hint: that means I don't have this problem. )