Ratio of Support Person to Multi-user Customer

So there has been a lot of discussion about the (lack of) guidelines re number of Techies needed to support number of users BUT what about this…

Software vendor supports customer. Customer has many dozen, if not hundreds of, users but they have first level of support covered. So vendor only gets difficult questions that involve bug reproduction, configuration changes, data fixing, and so on. In this environment I find the ratio of Support Engineer to customer (not individual user) is nearer 1 engineer to 15 customers. Has anyone any input/comments on this?