"Ground Idle" - (Approximately 10 degrees coordinator travel) is a detent position. This is the ground operating position at which blade angle is set for minimum thrust.
"Ground Start" - (Approximately 18 degrees coordinator travel) is a detent position. This position sets blade angle for engine starting.
Maybe it is G model stuff only. Less blade angle drag. Probably would work with the older models as well(at leat with 54H60 props) but no detent for positioning the throttle, only guesswork.