Groggy,
I have operated a fleet of IO-520 piston twins for years. Over that time I have probably gone through at least twenty engines which I have run to 2000 hours TBO (CASA approved). I have fitted them all with Gami's. My pilots have been instructed to run full throttle at 7 - 10 thousand ft and 2300 RPM. leaning is 50 - 75 ROP. Yes they will run smooth LOP but I have forbidden such operations as to much power is lost (read speed). We have never had any problem with any of the engines other than a heap of those rubbish ECI cylinders cracking a few years back.
My point is that running 50 - 75 ROP is great and will not damage your engine in any way. The POH does not suggest running LOP.
Groggy
You are operating at 65% at 7k at the maximum, and mostly less so sure you can run 50-75 ROP and with Gamis run accurately there.
Can I suggest you attend either location. You will soon see that despite the good results you are getting, you are operating where peak pressure is at its highest and not achieving best power, through to where max power is achieved. Yet for a very slight reduction in speed you will have much healthier ICPs and much lower CHTs and save around 20% of your fuel bill.
With good climb technique you may improve operations there too! You are close to optimal operation but not quite there.
I fear you may be almost seeing the facts and data but still hanging onto a warm fuzzy feeling of a superstition. Seeing the data generated before your own eyes is a truly enlightening experience, and nobody else in the world is bothering to do it.
As for the reason why the POH does not mention the other half of the graph, that is because stock engines, which yours are not, could not operate there. Pilots and their wives or pax do not like engines that run rough. So that half of the combustion curves was just simply org noted as unreachable. This is the truth.
400,000,000 plus hours of airline data, plus the unknown more flown is not evidence enough. You need to sit in my seat, come do it to my engine, all the data in front of you.
Take up the Deakin challenge
