Loiter settings for large drone 15 kg

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e are now testing our drone in auto mode; it overshoots the WP quite dramatically and then also needs time to find the radius of 1 m WP. When it turns it starts brusk and overshoots by 90 degree at least, then it has to move back, etc… We have the Loiter Stabilize P at 0.5 and the PID at 0.2 and 0.02. We can use the D. More important we cannot further reduce the I value. So we then thought getting in the WPNAV and reduced horizontal acc rate by half, but question if that if is for yaw too? If we want to use bigger crafts even, with more inertia, how we be able to change the I for the Loiter mode?

With the drone we plan to make waypoints in row patterns so that we can spray: results so far:
way points positioning of the drone takes few seconds, Accuracy is not good enough (although 17 sat)
Should we replace the jig saw pattern might be replaced by turns?

Can the experts help us how to change the I value of loiter P (PID) to lower than 0.02? and the radius of the WP to 0.5 m What is the generic effect when you fill in parameters below or above the boundary values.