If the shirt, is TOO small (not just neck but body too), we do scale the collar down.
We were doing it for bigger shirts earlier but stopped the practice.
The problem is that dimensions are mentioned on the website for some collars. If we change that without customer consent, the customer can and often does complain. Writing to customer (Hey you are a big man, do you want bigger collars?) is not always a good idea either.
So, if you know what you want, best to...