All-metal locknuts: how much thread is too much?

There are specific rules on the minimum number of threads that should stick out of a nut. Can’t use a bolt that’s too short.
Here’s one that I’ve not seen discussed and can’t find anything about online: how much bolt stick-out is too much? People usually say “well if it’s more than 10-20 threads it’s ugly and liable to be a hazard” but what I’ve not seen is a rule about locknuts. They deform their threads as you tighten them, which is why they lock, but after enough tightening, they’ve plastically deformed enough they don’t lock anymore. (Which is why you don’t reuse them.)
On my car, I have, for unknown reasons, six places (the tops of the front suspension shock towers) that have 1/4"-28 studs sticking out, that are probably 1.5" long. When I put locknuts on them and tighten them down against the shock tower, there’s 25-30 threads sticking out, and the locknuts are definitely way looser than when I started tightening them down. I think this is dumb and unsafe.
Does anyone know any guidelines on this?
(I suspect the car originally shipped with two jam nuts, hence the stud length, and I have an aftermarket manual that lists a locknut because they haven’t actually done the work themselves, just looked at it and made an assumption.)