The Sales team for new customer acquisition composes of two well defined individual contributor roles other than the head of sales function.
In the inbound Sales Model, customers are interested to talk to technical people who can help them in succeeding. They are not interested in talking to "Sales" people. So, it is important that some with the right "touch" and right "feel" engages from the beginning. So a title like "Technical Account Manager" helps a lot to get away from the "Sales Scare". Now this is *not* just a title change. It is genuinely creating an organization that help customers succeed as well as close deals from the vendor perspective. That is why this job is titled as "Technical-Account-Manager".
Now, in inbound model you are expected to get 100s of new signups in a day and many of those signups will have to be pre-processed before it hits the Technical Account Manager. Otherwise the TAM will be de-focussed on calling invalid signups etc and be less productive. One inbound SDR can support upto 3 TAMs. This number has to be adjusted based on the type of product. This can be 1 : 1 or 1 : 5 depending on the complexity of the product. Also an inbound SDR can handle 400 to 500 leads for a rolling month.