The size of the tire is not a determinant of air pressure, the air pressure is not measured in volume, it's measured in pressure exerted on the tire and is determined in very broad terms by the weight of your vehicle,
in my experience, your pressure should be a MAX 27 psi, at first it might seem a bit strange to you as you're not accustomed to it but in my experience 27 is more than enough for your car and if you're doing sand driving then deflate to 22... but re-inflate when ur back on tarmac.
After inflatin gyour tire, get on knee behind the jeep and look at the tire from behind keeping your eye level around 15 inches off the ground, and compare it to the diagram attached. (I took the diagram off the net)