A proper nut slot is based on your string size and the correct height of the string above the fretboard/fingerboard.
A properly wound string comes off the post just above (but not pinched against) the bushing.
The two are in no way related.
If both of these are correct, but the string still sits high, this is due to poor design (not a problem with Fenders, in my experience) and, then I could actually see adding extra string trees/guides/retainers to compensate, but otherwise, it makes vastly more sense - and it's more economical - to simply wind your strings properly.
Foolproofing is (aside from design issues) for the inexperienced player that doesn't wind their strings properly. And, if you have visible post under your string, I'm sorry, but you're just not winding your instrument properly.
I'm not trying to criticize. I'm trying to help. This is something that I learned in one of my very first music lessons (and something that all bass teachers should cover in initial lessons), and I'm just trying to pass it on... that, and I've seen many posts where proper winding completely solved the OP's problem.
Still, I'm sorry if I've offended anyone. hrb