What a great topic.
A few misconceptions MANY pilots have....
Manifold Pressure: It is technically a pressure guage. BUT, it makes people think of pressure in the case, when it's almost always a vacuum. The engine is always able to run and handle full atmospheric pressure. The air being drawn into the Filter/carb/throttle body/intake whatever is always from the intake stroke of the engine (with minor ram rise "dynamic loading" from moving through the air.) You can't "overboost" a cylinder with standard atmosphere (no turbo/supercharger). Never. The engine is always most efficient at WOT (wide open throttle), when one is not limiting or starving the engine of air. There are other factors of course, but that's what makes 8-9,000 feet with WOT such a great altitude for most normally aspirated planes. Anytime the throttle is at less than WOT, you are limiting the air that the cylinder is "drawing in," So, at idle - 12ish MP, the engine is getting very little air, but not fully cut off - the engine wouldn't run.
Fuel Enrichment at full throttle: A lot of people think it's for engine cooling, and that is a secondary benefit. But, the fuel enrichment at WOT is another detonation avoidance tool. It's designed to slow down the combustion event on the power stroke at high power settings. That's really it. In cruise and even take off, you can use the mixture to set exactly what YOU want (best power), but being slightly on the safe side is better.
Oversquare: Again, the idea that you overpressure the cylinder with prop back more than manifold is wrong. THE PROBLEM is and always has been detonation. Most of our engines are tuned for full Take off power. Otherwise, we'd have variable advanced timing, fadec etc. Setting our timing for full power takeoff means we make a compromise at other settings, especially towards lower power settings. I personally like and have used leaving full throttle and bringing the prop back first. 2700 RPM to 2500 RPM is an 8% reduction in Revs. 2850 RPM to 2,500 is a 12% reduction in Revs. At sea level with full MP available, bringing the RPM's way back creates a situation where the engine is running slower (cycles/revs) but getting full power from fuel/air mix. The combustion event has the possibility of completing earlier in the power stroke. Think of it this way. At 1,400 RPM the stroke takes twice as long, but the combustion takes the same amount of time. You in effect are burning your power earlier in the stroke and you're PEAK PRESSURE POINT or PPP, happens at a point in the stroke where you don't get all the BANG for your buck. So you're running the risk of losing HP because you didn't hit your optimal power point in the stroke and you run out of combustion early, which leads to detonation.
I have a cool chart image from GAMI that I'll try and insert.
USE at your own risk.