Trying out a number of metal headjoints, I noticed some in the shop were very different from my usual chimney.

One of them was caved inwards. It seemed to play very smoothly with a mellow tone. Not as loud as usual.
The Yamaha 784 standard headjoint is very plain and straight - but it has a great sound, without sounding brittle. This is probably my favourite.
Another one had an outward curved lip plate, so that the lip only makes contact with the central portion of the arc. It was very loud and responsive.

Does anyone know what the differences in the shapes of the lip plates entail? I know it makes more sense to try each and every one out, but the shop keeper is getting impatient with me lol.

Does anyone know what the differences in the shapes of the lip plates entail? I know it makes more sense to try each and every one out, but the shop keeper is getting impatient with me lol.

If he/she gets impatient, so you should look for someone else. He/she is not the right person to assist an instrumentalist to find such a personal, individual thing like the headjoint of your life.

About the different designs of embouchure holes, this is known as the biggest secret in the flute world. Builders keep it for them and every one have their own solution and style. That's why it's so confusing to choose a headjoint, because even if you take two identical headjoints, still there are noticeable differences that make you choose this or that one.

Take your time and really experiment as many as you can and for the time you need. Each flutist has also a different timing to assure finding the "one".

There are no secrets that a set of measuring tools cannot detect on any headjoint known to Mankind. Also, you shouldn't judge a headjoint simply by the lip plate. It is but one factor of a bunch of things that work together. These include the shape and geometry of the hole and height of the riser and its geometry, and the tube taper. (among other factors as well, but these are the most critical.)

Joe B