what do you mean by “co-bcch” ?
usually, co-bcch refers to two neighbour cells using the same bcch ARFCN, and is therefore something that one tries strongly to avoid.
On the opposite, you seem to rather enjoy it. I suspect you are either sabotaging your own network (:-) or using this term incorrectly.
do you mean “multiple CCCH timeslots” ? or colocated cells ? or multiband cells ? or SFH 1×1 ?