FlightOne PC-12 AOA

Using 15 deg. of flap and gear down, if I approach at book approach speed of 98 knots, approach seems correct ( power back to 5-10%)......but if I center AOA, speed decays to approx 89-90 [which is 30 deg flap bookspeed??]. Am I doing something incorrectly? Thanks for any advice, Bill.....btw: This is with FlightOne PC12.