Hexacopter stop at Waypoint Bhehaviour?

Hi to All

My hexacopter flies well and perfectly stabilized , hover and well tuned.
Pixhawk 1 with AC3.4.6
ublox GPS m8n
BUT when i try it in AUTO mission it destabilize to stop at each waypoint trying to cut its speed.
I want it to start reducing its speed 50m before every waypoint so it flies stably.

I know there is a parameter to be used in AUTO mission (WPNAV_ACCEL).

BUT is there a parameter like (WPNAV_DECCEL) to reduce the speed before reaching the waypoint.

Do you have a time to stop at each waypoint set by chance?

i do not know??

How could we that.