So RH recommends a substantially higher tire pressure, which I would not have guessed. I think this is possibly because the sidewalls are so thin.
I've also noticed with my 42mm treaded tires that they work substantially better (no slipping) in loose gravel/dirt if they are inflated higher than recommended, which is completely counter-intuitive and contradicts their own recommendation to let air out for gravel.
The pressure calculators only get you so far.