I saw this and thought of a good drill to help practice for this situation, even though these situations are completly random this might help.

1.Find somthing u can vault over (maybe onto grass) but can't see the other side untill ur right there.
2.then have one of ur friends (if u got any, jk) put a Percision jump trainer (they are easy to build) in a random position on the other side.
3.Vault and try to land on the bar.

This might help, but when ur out there it could be completly random. this might help a little.

Alright, thanks a lot it all sounds great and I've tried a lot of it. For the particular described problem (mostly a vision problem) i found that a monkey works the best. For the mid-vault adjustments ive found i really like the lazy. So thanks for everything!