Paul,
Even on the half and half castor/synthetic oil fuels, there should be some visible exhaust "smoke" or vapor. There's less the leaner you go. The modern ABC, ABN, and AAC engines get plenty of lube from the popular 10%-11%-11% fuels, and should not fry.
Check with a tach for when you get into steady 2-cycle. Except for older style engines like the Fox 35, there should be well over a thousand RPM from that point until needling in doesn't increase RPM. On a light load prop and 10%nitro, 11%/11% castor/synth fuel, the range in steady 2-cycle may be a few thousand RPM .
The prop unloads as the model comes up to flight speed, and on 4/2 run engines, IMHO, it is that unload that sets the 4-cycle level flight mode. For engines designed, basically, to run primarily in 2-cycle, you might hear an occasional 4-cycle burp if you set it low in the 2-cycling range.
Anyhow, "wet" 2-cycling has ample visible exhaust, and is low in the engine's 2-cycling RPM range. "Wet' and "low" 2-cycling are pretty much the same.
You may need to train your ear a bit if you run mostly in 2-cycling. You will hear it strain a bit if you're set too high in the RPM range, particularly in the Overhead Eights and the upper loops of the Four Leaf Clover.
Since low-pitch prop, steady-2-cycling is pretty much like running in first or second gear in a sports car, there's plenty of power (higher RPM) at reduced flying speed. There's no reason to use less than all the power you can get that way, short of hearing it strain more than rarely. In that case, richen a couple of clicks, check RPM, and see how that sounds.