The hover and top end needles must ALWAYS be adjusted in consideration of each other. Though the two needles adjust in the range for which they are named, the hover needle's fuel contribution remains in place even as the high speed metering takes over. Because of this, if you have the high speed set and then make a major change in the hover needle, you better be very careful when you go back upstairs to avoid having a lean run.
I've flown for Performance Specialties for several years now with both STII's and the 80's, and I've never noticed a significant impact of the idle adjustment on the rest of the throttle range UNLESS the idle needle is set way too lean. In these instances, the motor will tend to go lean in hover if the throttle curve postions the barrel anywhere below the hovering range on the carb. This tendency is largely due to the transtion back into the idle metering on the barrel and not due to the contribution of the idle needle to the fuel supply during hover. This concept lies in relative contrast to the classic tuning methods of more conventional motors like the OS 32 where the idle needle is used to optimize the hover mixture along with the high speed.
I was fortunate enough to have Rick Mattie, who used to be the YS tech for Futaba when they distributed YS, explain to me in person the workings of the YS carb and how to modify the barrels to suit my needs if needed. The lesson took over an hour, and I wouldn't trade that wisdom for anything.