Are there any good guidelines for orienting the curved head. The two extremes seem to be:
Vertical - the lip plate is mounted directly above the tonehole line, rotated to align the opening as with straight headjoints
Horizontal - the curve is parallel to the floor and moves the body of the flute away from your body.

Neither one of these seems right...I have been practicing with the headjoint about 30 degrees rotated towards me from the vertical position with the lip plate in the proper position to blow. This seems like the best compromise of balance and arm position.

I just received this curved headjoint for my recently acquired Jupiter alto. I don't really find any big tonal differences (pleasantly surprised) but I do find that the 2nd and 3rd octaves are about 15 cents sharp from the bottom octave. The straight headjoint is perfect in this respect, so I'm reasonably sure it is the headjoint.

I've seen most people have it at an angle, as you described. That is what is most comfortable for me when playing my alto and bass flutes.

You should just position it however is most comfortable for you.

It's a little tricky to get the balance right.

I like the placement somewhere in between horizontal and vertical say 45 degrees for a mid point. You also will need to rotate the blowhole so that which ever is a comfortable balance, the embouchure hole is not rolled in or out uncomfortably.

If horizontal, it's too hard to roll if necessary. Too vertical for me is uncomfortable on the wrists.

When you get it the way it's comfortable then mark it with tape or a mark or some reference to put it in the same place each time.

Comfortable is MOST important though. Rotate the curve for balance first, then roll the headjoint for good playing position.

Joe B