How many customers have come in with the "loose acoustic jack" problem? Lots, lots, lots! There's a reason they loosen-up from the endpin/endblock area -- it's because there are too many extraneous parts that move. Above I've removed the jack from the guitar and you can see the lock washer and plain washer. The first step is to remove those...
After that you can figure out the depth you need on the remaining hex nut (which will hold the inside portion of the jack against the endblock) by pulling the jack in and out until you decide where you want it.
If I have enough thread, I'll then screw the cover on the inside of the jack right behind the hex nut and tape both of them off with duct tape to keep them from 1) rattling and 2) in place as I put the jack back where it should be.
"Proper" extended length of the small-threaded portion of the jack should have said small portion starting just a little below the surface of the guitar. This is because as you tighten the jack up, it will pull forward into the wood of the endblock and you don't want to run out of thread to tighten it.
As it pulls the hex nut into the endblock, the angular nut's shape will press itself nicely into the wood and give a better grip vs. the plain washer and lock washer that were previously on it.
Fortunately, most of these acoustic endpin jacks feature a hole in the side to stick a gadget into to hold it still...
...as you tighten it up. Feel free to crank on this to get it as tight as you can (within reason). The outside "endpin sleeve" can then be tightened over this bit.
On guitars, ukes, mandolins, etc. that have awkward bodies to push and endpin jack into its hole via the soundhole, one can use a bit of string going into the jack hole from the outside which can then be pulled-out and tied to the jack's end before insertion into the guitar.