Hi,
Thats based on the JR system and has the same menus as the JR3810, I think. The below 50% RATE mode, over 50% heading hold mode method applies here.
Check you have the limit pot on the gyro as high as you can get it without binding at max control throw with the gyro set below 50%, as here the servo will act normally. Remember to reset it before flying.
Also your rudder travel adjust should be around 100% each way. If you have had to set it very low, move the ball on the tail servo in a hole and try again.
Also, have you set your gyro gain by flight testing? or is this just your starting point. It may need to go higher as long as the tail dosen't wag you are OK.

Hope this helps.