rosa,
sdcch assignment failure rate due to radio problems = 50% is NORMAL if your ABIS (or ATER) are over VSAT.
There is nothing you can do : the MS sends a CHANNEL REQUEST, but by the time the BSS replies with an immediate assignment message, the MS has already sent a second CHANNEL REQUEST. This is an internal MS timer, which is too short. You can’t change it.
Therefore, consider this value “50%” as your reference for VSAT cells.