Should be closer to 32 psi, all tire sizes, unless you are carrying four people and a full load of luggage. Then the owner's manual says to take the rears up to 39, but to keep the fronts at 32. 20" tires do not require higher pressures. That is from my 2003 model owner's manual, not sure what year you have but it should be similar.

Too high a pressure is definitely not safe. And if you have moisture in the air from the compressor, you will get more variation than if the air is dry, as it is the moisture that expands more so than the air as the tire heats up. The sensors are seeing a variation between tires, not just a low pressure, so too high a pressure in one tire could cause the sensor to go off as well.

Suggest you set all tires to 32 psi cold (or 35 if you insist) and then see if you continue to get nuisance warning lights.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue