Radio Failsafe - can't set low value

HI All
Hope this is the right area!
I am having trouble setting the low value for the radio failsafe, I’ve kind of worked around it but was wondering if there’s a better way. I’m using the FlySky FS-I6 TX flashed with the 10 channel firmware, and a FS-IA10B RX.
Setting the failsafe value on the TX only goes down to 100% - so when the TX is turned off, the RX goes into failsafe mode and drops the throttle to the -100% value, 1000, which isn’t enough to trigger the failsafe (set at 975). It just looks like you’ve throttled down. So what I did on the TX, was slightly raise the lowest value on the throttle curve by about 2%, which means that when the throttle is in the lowest position the PWM value comes across as around 1020, then recalibrated in Mission Planner. When the TX is turned off, the value then drops to 1000 and I can set the low trigger value to 1004 which then triggers the failsafe.
This all seems a bit kludgy, is there a better way, or is it just a limitiation of my radio setup?