My guess is that neither is correct. The actual resistance of 3/16" line varies quite a bit between materials, manufacturers, and even between different runs of the same line from the same manufacturer. My experience has been that the actual resistance is almost always less than even the lowest published values. IMO those calculators aren't good for much more than a very rough estimate, if that. My suggestion would be to make the lines much longer than you think they need to be, and then trim them down if it pours too slow. It's very easy to cut a few feet off of a line that's too long, but making a short line grow longer is a bit tricky.
FWIW I made all of my lines much longer than needed, and the only side effect is a slightly slower pour. I'm not running a busy bar where how many beers I can pour in an hour matters, and if I have time to drink a beer, I have a few extra seconds to wait for it to pour. And if I want to serve something very highly carbed, it's not an issue, and will pour fine without resulting in a glass of mostly foam.
There are a lot of recommendations on this forum to start with 10-12' of 3/16" ID line, but most people are also serving at 10-14 psi. For your 20.7 psi, you're probably going to need quite a bit longer. Even with long lines, keeping 3.0 vol from foaming at warmer temps like that may present a challenge.
Hope that helps, and good luck.