I understand your situation, and it’s a classic NW application. But it’s not the same as Erlang B. NW assumes that the the peakedness comes from another trunk group that is in an ATB situation. The big peaks (and non-random traffic) occur when the primary trunk group (not the one under analysis) is ATB.
Extended Erlang B is different. It only considers one trunk group and assumes that if a call encounters ATB, that a percentage of those calls will retry. But, the generation of those calls is random, albeit that the offered trafffic is a little skewed when the blocking is high.