Baseline differs from design to design, even differs from model to model of same design. Been my experience. Been the experience of flyers I've flown with. Also depends on engine. Some engine designs are more tolerant than others, more forgiving in tune. Others less tolerant. LA46s, LA25s seem to have a wider comfort zone. FP 40s, better get it right. Profiles frequently, full bodies less so, are subject to vibration gremlins. I've seen perfectly fine running LA46s, get weird when switched from one profile to another. A club member gave me a nice looking Skyray, turned out to be another example. Powered by a decent running FP20 with stock muffler etc., wouldn't pull plane through a wingover. Could have been line length. Didn't seem excessive. Hours were spent trying to get the power up enough. An Fp25 with a tongue muffler, no problem. Still a nice flying combination. Folks have reported better results with FP20s, stock muffler, venturi, and so forth. There's also issues with engines running differently in different locals. Engines running differently at Carmichaels than in Philly. Bedeviling. Needed to be retuned. Higher nitro helping. Again. Some engines more sensitive than others. Also, issue of wear. I've had LA46s run fat and sassy for a long while. Then become erratic. All usual suspected issues looked at. Clogged filter, loose something or other. We think it was front bushing wear. Engine was tried on different planes, different tanks. Also, on other end, issue of break in. Well broken in engines calm down, run better, even incrementally. Even true for those engines often though to not need break in time. FPs, LAs, run well at first, then run better.