All else being equal and for any given tire, internal pressure will be the major factor in contact patch size. But you can't compare a narrow tire (say a 195/75-14) with a wide tire (say a 315/35-20) at the same pressure and think they will have the same (or even similar) contact patch size. The 195 is less than 7" wide while the 315 is more than 12" wide. The tire shape doesn't deform enough to account for that difference. If you want proof, go out in the parking lot and look at any tire on any car - the tire contacts the road across the entire width of the tread. That means the 315 contact patch is at least 5" wider than the 195.
2011 Pony Pkg. convertible M6
Am WS7 (sold)