Thats strange
One my tranny my setting for brake is at 3% but then thats how i set it at and its strong enough.
Have you got it set at these settings ?
Description other names in radio Required Setting
Throttle Travel High ATV, EPA 100%
Brake Travel Low ATV, EPA, ATL 100%
Throttle Exponential EXP, EXPO start with 0
Neutral Trim SUB Trim centre
Servo Reverse Throttle Reverse any setting, don‘t change after set-up procedure!