This is the siemens names of the row counters, I dont know what are you using for network monitoring. A is attempt, S is successful if you sum all attempts you could see what is the share of LU attempts, If you sum successes you again see the share of LU successful.
ATIMASCA (1,9): Attempted Immediate Assignment Procedure
This measurement gives the number of times an immediate assignment was requested.
Different counters distinguish between the assignment causes.
Attempted immediate assignments of an SDCCH:
Counter No. Att. Imm. Assignment with Cause Valid for MS Phase
1 Answer to paging 1+2
2 Emergency call 1+2
3 Call Reestablishment 1+2
4 Other services (Orig. call, SMS, SS)
5 Location update,all other cases
6 Other procedures (IMSI detach, SMS, SS, etc.) 2