Yeah, it's my experience as well.
And, while the "floating vehicles symptom" as occasionally witnessed in the Zone has been referred to, then I think it's the time and relevance that I should this:
Actually floating vehicles matter has been resolved (in fact it's on 2.4 as well) by the inclusion of
barin's ingenious script.

(as far as I'm aware, OL and some other mods also use that script.)
-you may still see some vehicles float, while they had not been floating before, strange? No... This is how and why-
1) This
barin's script
hits the vehicles upon the actor's entry into the level, as if you are hitting any vehicle. You know that when you hit or shoot a vehicle it drops down if it was floating before.
So they come down to the ground. (This works on the vehicles that are spawned through the all.spawn)
--but..NOTE: as it always happens with Xray engine, and that it is a bit senile and forgets almost everything after a reload, when you reload the game in that particular level, the game does not always (mostly) remember that the vehicles in the level had been hit. Here they go floating again.
If you die or whatever reason you reload the game on any level, so you may see vehicles back on the air.
2) Some vehicles that are spawned by script (not by all.spawn, like GSC vehicles) cannot be hit by barin's script, as I see, because they are created (spawned) by script commands and because of that it's not possible to enter section names as opposed to what can be done in all.spawn. So, then this
blow/hit wave in the air misses those vehicles that are spawned by script commands.
PS: important info: But I've managed to make
our APCs (all are spawned
by script commands, not by all.spawn)
stand on the ground on their very solid tyres, so to speak,
without floating.
However, if you reload, like all other vehicles they will
become prone to float, as Xray will prove its senility.
So notice that they are solidly on the ground as seen in the pictures that I posted in previous pages.
(PS-2: We have now
13 more APCs in v3.0, making the total, say, what, well over 20. Hmm,
27 I guess, I need to recount, lol)