In general if the pilot gives maximum left or right steering input the desired turn rate should increase to the ACRO_TURN_RATE value. Two things to be careful of though are that the ATC_STR_RATE_MAX is the same or higher than ACRO_TURN_RATE. The other thing to check is the ATC_STR_ACC_MAX value. This could slow down the rate with which the desired turn rate increases.