It would be the flange as the front of the camera is irrelevant to that measure as no adapter goes to the front of the body but stops at the flange.
I think they refer to it as the faceplate- see the measure for the Proline at 21.3mm :
http://www.flicamera.com/proline/index.html
You need this measure for an exact adapter? I am sure it would be safe to assume its "around" the 20mm band if there is a tolerance factor.
I can't comment on the poor service other than my experience with FLI has been great. Who knows perhaps that guy has gone on holidays. Greggory Terrance is usually very responsive. Also Richard Crisp (not a FLI employee) on the FLI Yahoo Group probably knows as he used to use one.
I've posted the question there and I'll let you know if I get an answer.
Greg.