Hello! From what I know, all they need to do to see your preset is to put the .fhp, in the main FH folder, in "presets". Not "my_presets", but "presets."
Are you sure they've done that, the people who have the sync? Because that's the only other way to see your preset, is if your .fhp is in both your "presets" folder and theirs. The only other thing I would suggest is to try re-exporting it?