Failsafe value for Stick mode 1

Hi, I am having issue with failsafe for rover, I am using PIXHAWK 4, FlySky FS-T6. I wanted to use throttle and aileron with its right hand so using Stick mode 1 in my radio. The reason is to use my rover in both direction, forward and backward and stop in the middle, its PWM value is around 1500. Its working fine but in failsafe if radio disconnected, wheels spins very fast and in failsafe configuration, it is not accepting value 1500 and the range shows 1100 and less. I am stuck dont know how to handle this situation. I want to know the correct method or value for failsafe in this scenario so when my radio switched off, rover should stop or RTL. Please help.