That is normal. When oil temperature increases, its viscosity goes down (=is easier to flow through the engine galleys and bearings). Generally, if You're within specs, then You're at the safe margin. While getting to the edge, You may either:
- rebuild the engine bearings (materials ain't expensive, just the labor) or
- use a thicker oil (like 10W30) to compensate the pressure with a higher viscosity, but it's a half measure, that might affect the life span of the oil pump.