Single rotor helicopters will always have a miss match between being in trim with the ball centered and sideslip angle. This is because the fuselage has to balance side force produced by the thrust of the tail rotor. It is particularly apparent at slow speed high power settings when on the back side of the power curve. I fly in trim because there is no way to display side slip angle unless you have special instrumentation. You can put a piece of yarn on the wind screen and with a little practice negate some of this annomolly by playing with pedal position, but I think it is more trouble than it's worth in the Huey I fly. Maybe it might be more usable in a R22.