Throwing this in here just in case; make sure that when you log in, your username has the exact capitalization of when you exported it! For example, if you log in as "chimmy" but you exported the preset as "Chimmy", you'll run into some problems.. It's pretty odd.
I imagine this might be a problem with sync itself, if the person who doesn't use it can see your preset. In my experience, sync sometimes deletes newer additions to any folders. It's a little finicky.
The people with preset sync should be putting the .fhp in "PrivatePresets", yes! If they throw it into "Presets" or "PublicPresets" (if the preset was donloaded manually), I've found that it causes issues. I wouldn't expect that you'd have to download sync as well! As long as they have the .fhp in the right folders, theoretically, it should work.
Cheers and good luck! This sounds like quite the pickle.
