I have. There is a good amount of variation between HF models with regard to focal distance after the flip. Some remain hyperfocal, mine focuses @ around 4 ft, the #13 diopter approximately halves that. You can work out the details with the old scotch tape trick.
HF flip + #13:
Oh! That is one of the reasons I continue to "stick" around here . . . good information. Wonder is a piece of velum might do the same thing, full frame? Perhaps I'll try that. Bill Barber
Velum will work or a piece of plexiglas that has a dull surface is good, too. I have a couple pieces of plaxiglas cut to fit different formats. I put scotch tape on them to give a ground glass effect. I just use a couple rubber bands around the camera to hold it in the film track.