The difference between Request and Success will give you oth congestion rejections and radio failures (or possible hardware failures).
The only way is to count the difference between Channel Request and Channel activation.
This way, the result only shows the rejections dur to congestion.
I didn’t know about the Imm asg Reject feature being so specific to ALU. And the worse thing is that it is disabled by default !
could you check the erlang per TRX, to detect unused TRX, perhaps ?