what you should ask is “what is the purpose of “bts pwr min”…?”
– this is the maximum attenuation that can be applied to the signal with power control.
there is no correlation with the bts pwr attenuation, which is the “minimum attenuation” (which allows to compute the max power) on the cell. When pwr reaches this value, it means the cell is transmitting at max power. Max power is used at call setup, just after a HO, or when rxlev/rxqual are poor and PC will push the power to the max to save the call.
Also, this max power is used by EGPRS transfers.