He analysis is based on Chicago but I think has some general patterns emerging in the structure of the data.
BM

A highly rated local provider that retired about 2 years ago thought it was about 3:1.

I think she was counting the number of different guys rather than the number of sessions.  I don't think she included a handful of regulars that saw her weekly when coming up with the 3:1 ratio.

We got on the subject because  when she was recounting a conversation with another provider about how the regulars that book weekly or a couple of times a week are the most physically demanding.

I think the ratio has gone up since 2008 because I think the great recession has changed peoples habits and the number of guys on TER.