All of the above aside, I think the original point was one of trying to sort of standardize how often this happens. In other words, you could hex the character's car/gun/whatever every time it's used. But that would get old quickly. On the other hand, those things ought to get hexed at least some times, too.
I suspect that setting a 'goal' of at most one or two compel-worthy hexes a session is probably about right (plus any number of 'ambiance' hexes as appropriate). And then let the player self-compel beyond that (keeping in mind that it doesn't count as a compel if its not an advantage).