I could swear that it feels like they are sometimes extremely difficult to kill when dropping. When on ground, no issues - but just had a guy survive a bolt shot at pretty close range while still falling.
Am I just getting extremely bugged hitreg or is there something weird going on with para health?
Nope. They are just as squishy in the air as they are on the ground.
I experience this as well, but I believe there is a simple answer as to why – on average, the paratroopers are much further away than other targets that I tend to engage with using the same weapons. When you combine the increased engagement range (which = greater damage drop-off on all weapons) with the fact that you shoot up at the paratrooper’s feet/legs as they fall and you end up with a much lower DPS overall.
But I can’t say for sure that you aren’t on to something. All I know is that it doesn’t feel like you get more health when your whole squad is dead before you hit the ground, so I’m thinking it’s a bit of a numbers game.
Also, just throwing this tangent out there, if you happen to drop your paratrooper supply crate directly on a strafing BF 109… you don’t get credited for the kill. The crate itself doesn’t do collision damage, but it can easily force a plane to crash. Which, I guess with the new “anti-kamikaze” feature could be even more beneficial to your team, but it’s pretty lame you don’t get the credit/xp. 
nop
2 things:
You’re shooting them while they’re 100+m away in the air, so dmg dropoff
You tend to hit the legs more, so the dmg gets reduced even more
Personally the thing still the same as in the ground like in the air the paratroopers can resist at least 3-4 submachine guns bullets…
I think i should improve My aim i always got killed in a cqb combat against them…
What? No chance, paras survive much more while in the air, you can’t be right about that one, or is it JUST that they are further away?
As Euthy said, it’s probably dmg drop-off.
They die just the same though. Done it many times.