Eeks I think 20psi is missing the point of plus tyres.
I’m a big guy and only get squirm below 12 psi, my sweet spot is around 13-14psi
Any harder and you may as well be on normal tyres imho. The grip and the bump absorption that keep you rolling faster just won’t be present at 20psi.
What tyres are they?
With respect to mud, yes they are crap at that… ONnly thing I found any good on the front in mud is a dirt wizard, but I did see a pic of a 3″ minion somewhere which may also work