After reaching my cruse altitude I set my power and turn on the peak detect system on my AFS 3400 Engine monitor. As I start leaning, the EGT temps rise until they peak. As I continue to lean the EGT temps fall, and at some point (well below peak) the display shows ROP. Along with a number that represents a temperature on the rich side of peak. While continuing to lean the display changes from ROP to LOP temperatures until the engine is not happy and I need to enriched a bit.
Hear comes the big question.

Why do I get ROP temps after the cylinders have peaked and not before?

I would think the ROP temps would show before the EGT temps reach their peak point. The only time ROP ever shows is after my EGT temps have peaked.