To remain below 2% GoS, a cell with 2TRX shall not exceed 8.2 erlangs.
Capacity of a BTS 2/2/2 = 3*8.2 erlangs
If cell with 2 TRXs exceed 8.2 erlangs, then the GoS will get greater than 2%
One TRX can accept up to 8 timeslots TCH, so that is 8 FR calls or 16 HR calls (and any possible mix in between)
When you talk about capacity of a cell with 2 TRXs, you cannot talk about the individual Erl. capacity of 1 particular TRX.
Erlang B Law doesn’t work this way. You must think at “Cell” level.