Smooth tune of WP Speed

Hi guys, I configured my CH6 to tune WP Speed during the flight and I use it to change the speed during autonomous missions with my long range copter so I can fly slowly across the wind and fly faster towards the wind. The method of the tune works pretty well. But one thing worries me. In the moments when I tune the WP Speed, I notice the sharp pikes by pitch. So I for example reduce the speed from 15 m/s to 14 m/s and in this particular moment the copter roughly twitches by pitch axis and stabilizes immediately and continues the flight. I assume it does it to reduce the speed but does it too roughly. How can I get rid of these rough twitches and make the tuning more smoothly? Thanks.