Tire pressure requirement is set both by tire construction and driving style. Setting it per the tag inside the door is OK for starters but here is how I "fine tune" (learned this from my earlier SCCA days). Once set to tag recommendation, take a piece of chalk and put a line perpindicular across tread and down about an inch on the sidewall. Go out and drive in your normal manner. When you return, check the chalk line and see how much is scrubbed off. The ideal pattern should show chalk gone from tread area and just onto the area the tread begins to wrap down to the sidewall. If you are down on the sidewall, add air; if you only scrubbed from the flat zone of the tread, let out some air.
Why would a tire require more or less air than the manufacturer's recommendation? Tire sidewall stiffness is a key factor and is set by tire construction.