Brian,
These gas engines will often not act very linear with the amount of throttle given. It is different from engine to engine and from engine/airplane/prop/exhaust combination to combination. If your engine doesn't seem to increawe very much in power from 1/2 to 1/1 throttle, it may just be your combination. I most often use a throttle curve for my engines (150cc and up), where 1/2 on the stick yelds 1/3 throttle opening. As you said, you very rarely use 1/1 throttle, so broadening the area you do use on your stick makes flying much nicer.

DKjens