It would be interesting to tell us what is the situation just before thhe call drop. Indeed, your description is really vague 🙂
which serving cell ? which band ?
which UL & DL rxlev, rxqual, TA ?
what about estimated traffic load in each band ? congestion ?
what is the cause of call drops, in your QoS statistics ?
what about handovers before call drops ?
if you are using HCS and multiband cell, it is possible to increase the probability of call drop in some lower intereference areas, the HCS and multiband cells normally causes to increase the call drop, even in low interference areas.