So made a prototype with the shortened breast point with a 3 part cup. I didn't even bother attaching the wires because I believe the wire is too large for my breast root and therefore the lower cup is too big no matter what I do. I also have a tension line through the cup that starts at the apex and right down the middle. I believe the apex needs to be moved over but if the volume of the cup is too large then all it's doing is trying to pull the entire weight of the breast up on its own. Obviously not correct.
Next up I'll either redraft the cradle for a narrower wire or draft a soft bra instead and forgo wires. I also get another annoying problem. The wire casing and elastic on the band where they meet tends to rub my ribs sore. At first I thought it was the band being too loose so the weight of my breast was causing a pressure point. But after tightening the band as much as possible, it doesn't change anything and it's seriously painful if I sit or wear the bra for a period of time. Is this a problem with having too big of an underwire?

My guess would be that yes, it's rubbing because it doesn't fit right. I mean, sort of by definition if it's rubbing or pinching or sagging or whatever, it doesn't fit right. So keep at it. Definitely draft it up for a smaller wire; if that's really sitting snug and solid against your breast root, then the whole thing should be a lot more stable and less prone to shifting and rubbing. Or at least, that's what I would expect.

I'm in the same position, extremely large bust/smaller ribcage (37M/N, which people think can't exist naturally). You may need a smaller wire and have to ease in the proper cup on the underwire line to make the bra work. If the mass of your breast tissue is small at the base but expands just after (similar to a balloon held against a flat surface), you may have an "Omega" shape. I have gotten alot of helpful answers about how to fit this (read: my) type of bust from the Bra Maker's Manual by Beverly Johnson.

You may even need to make the lower cup in more than three pieces. The more seams you have, the finer the fit. The prototype I'm working on didn't give me the lift I desire but when I subtracted width from the other three panels to create/add a fourth panel, everything started to curve up and round out better for my shape (yea no torpedo boob!)

Also try buying, or at the very least taking pictures, of bras you like the end result shaping of. I like the look of Ewa Michalak bras, especially the CHP and the CH styles. Even though it's a custom designer bra company, I still fall out of the range of their sizing. After studying the pictures and looking at some physically, i was able to see what direction I needed to go in. Plus looking at the fabrics they chose assisted in my being more selective about the fabrics I would use. Fabric makes a difference too.

Yes! I would definitely say it's an omega and am dying to get Beverly Johnson's books. I've made numerous bras and none of them fit right. With each one I'm finding out I'm even bigger in the cup size range. Some would be happy with this, but it's actually not fun when you can't find your size anywhere. Now I'm pretty sure I'm either a 34O or P US size. Good luck finding that anywhere. I haven't given up but with the number of hours I spent trying to figure it out, not much else was getting made. I made a few soft bras that fit but just don't give the support I need. Being short in the waist, no lift is not flattering. You can't see your waistline if your boobs hang too low. So right now I'm defaulting back to my nursing bras which give me the best support even if they are a little small in the cup. Also have had to take the band in. I've done a lot of reading on the wrong bra size and how back and armpit fat can actually be breast fat that migrated away because of ill fitting bras. So you can recuperate volume by getting the right size and scooping from back to front. Can even help lift breasts again. I think the fact some wires dig into my ribs right under the breast is also part of the short waist problem. I don't have that space for things to lay completely flat.

Ceciled, you might find some solution in Bra makers manual by Beverly Johnson on page 135-137. There she is writing about alterations to the bridge. If the bridge is too narrow in the bottom it might tip out from the body on the top.
I have about the same shape and problem, but splitting the bridge a little at the bottom made the bridge come closer to my body. Don´t ask me why but it helped!

This is a great question and study. I recently purchased a 1950's-era vintage torpedo bra thinking it would solve all of my problems, ie, keep the same under bust circumference (36) and mold my boobs (D+) into a period-correct shape for 40's/50's dresses. I was so wrong!
My breast tissue didn't conform into the tips of the torpedos, even though I thought I'd purchased the correct size and I have ample tissue to fill it out. My breasts are rounded and even in a conical bra, they stayed rounded, much fuller at the base. (Much to my surprise.) So I will be following this thread and any related bra articles with interest.