My ES-P has a TSIO-550E with GAMI injectors, and i've recently been through advancedpilot's web LOP course.  But I'm still unclear on at least one point.

My TSIO-550E will happily run at 17.5 GPH at a MP of any of 30, 31, 32 (among others).  All cylinders remain below 380, and TIT is reasonable.

My understanding is multiplying 14.7 x GPH yields HP, in this case 73.5% power

Is it 73% power no matter how I set the MP, so long as temperatures remain in control?  If that's true, why would I select one MP over another (realizing I can't run wide open throttle)?