I'd follow the manual which should have recommendations for each tire type/size. Normally if it's R4 tires and you're doing front loader work, the manual recommends numbers that are close to or match the max inflation of the tires.
No way it was 100psi for the fronts -- the 100+ number you saw was probably in kPa, not psi. Look closer for the equivalent psi rating on the tire. They always put both on the tires.