ED, ultimately all models rely on a series of assumptions, any one of which may not suit your particular situation.
I anticipate that at the ‘small end’ (less than 10 operators) most models will give similar staff levels anyway (whats the difference between 9.2 staff and 9.7 staff?)
You also have the politics of your operatrion to consider, in a 911 centre would ‘understaffing’ be tolerated?–peoples lives depend upon it.
Then there is the problem of the ‘civic disaster’ when all predictions about calls will probably not match the real events. Make sure you have a good contingency plan!
As your adviser said, most of the call centres use ERLANC C for predictions. There is safety in conformity !!