I found this manual for the BetaFPV Literadio 2:
However it doesn't mention anything about whether any setup adjustments is possible regarding the endpoints. My suggestion would be to contact BetaFPV directly and ask them if/how you can change the settings.
(FPV Freerider can only read what is coming in through the input manager. The input is shown as the little circles above the OK button as you go through calibration in Freerider. Ideally you should be able to move the little circles smoothly up and down between the lines on the left which marks the max/min value.)
(And yes, the pictures in the document I sent in the earlier reply is from what is seen directly on the screen of the transmitter itself, in this case a Taranis X9D).