The calculation of ROP, LOP, or PK next to % power is actually pretty independent of EGT. It's calculated in a unique way. You can actually turn on the EMS at 1300 degrees and it will know if that is ROP or LOP right away.
When you are first tuning the system, you need to use your EGT's to determine if it is finding the peak correctly. If it reads PK before you peak on EGT's, you need to adjust your HP number in setup so that it matches your real engine. The HP should be close to your rated HP, but can vary from the rated HP a bit.
Once you have it tuned, then the LOP/ROP indication should be very accurate when you are a bit away from the actual peak. It won't be specifically tied to a certain cylinder peaking or all of them peaking. If you're trying to use it right at peak it's not the right tool, although it does try and tell you PK when you are close.
The LOP/ROP at the bottom of the EGT graph is much simpler. Once one EGT peaks, it reads PK. When the last EGT peaks, it sees if you went up or down in fuel flow between the first and last one peaking, then it says LOP or ROP. However, this never updates once it determines LOP or ROP and requires you to go into leaning mode first.