Not that long ago, I ran into the same issue.
I've had many trailers, and I typically buy a ball mount and ball as a set and leave them together. So I have a tote baq with 5 ball-mount-ball combinations with various drops and ball sizes.
My previous high-wall popup had been lifted, so I had a straight ball mount "flipped" with a 2" ball on it. My current rig uses a virtually identical ball mount, flipped, with a 2 5/16 ball on it. Of course, brilliant me, I grabbed the wrong one and installed the 2" ball with my 2 5/16" coupler.
Tongue weight is heavy enough that the coupler stayed on the ball, but there was slop when on and off the gas. I left the coupler latched and ran down the tongue jack, and, of course, the coupler lifted right off the ball.
But grease on the ball prevented me from seeing that it was only 2". I came on this forum and asked about adjusting the coupler...since I could see no way to do it. Smart folks here told me to double check my ball size...no, not those.
With the proper ball, the coupler is a snug fit. Plenty of grease and a slight tug forward after dropping the coupler on the ball is all it takes for the coupler to latch. I, too, am fond of having the ball slightly forward of a perfect lineup with the coupler so the coupler has to pull itself over the radius of the front of the ball to drop on. Then no tug needed.
But don't take advice from me. I drove around with a 2 5/16" coupler on a 2" ball for several short trips.
BTW, if you grease your ball and coupler,
1) Always
cover the ball when not in use to keep the grease from collecting grit that will grind away at both the coupler and the ball.
2) Wipe of the grease on the ball and re-grease regularly. The grease still gets dirty. It's much harder to clean out the coupler, but that wouldn't hurt.
I like
spray lithium grease mostly because it's easy to apply...especially up inside the coupler.