Are these going to have the shirt clip? The fit on the similar FDX-1 is horrible without either putting over ear or (much simpler) a shirt clip. The over ear barely works anyway with that model. I see a JVC branded one which fits the special oval shaped rubber cable on their website, so hopefully this will include one.
That's all it would take to fix the fit, since a shirt clip would carry all the weight of the cable and prevent seal loss.