Hi Matias,
The timer T3122 is sometimes called wait indication parameter. There is no default value specified by the GSM recommendation for this timer, and I think it is depended on the hardware vendor. In the Motorola BSS system, the default value for this parameter is 5 seconds. I have no information about the attempt counter parameter.
You are true that in the LA border, it is reasonable to increase the SDCCH, bacause of the number of location updating attempt will be increase in this area.
Brgds