TCH congestion on ericsson GSM

HI,
There are few counters in the Ericsson GSM system for the TCH congestion.

TCH congestion:

100 * ((TFCONGSAS + THCONGSAS +
TFCONGSASSUB + THCONGSASSUB)
+ (TFCONGSHO+THCONGSHO+TFCONGSHOSUB + THCONGSHOSUB))/(TFCALLS + THCALLS)

Subscriber Perceived TCH Congestion (%):

100 * (CNRELCONG +
(TFNRELCONG + THNRELCONG +TFNRELCONGSUB + THNRELCONGSUB)) / TASSALL

I would like to know which one is the best for dimensioning purpose. I mean which one can be taken as blocking rate to estimate the offered traffic whith the carried traffic.

Thanks