Layered top knockoff - initial pattern development

Sleeveless tops, anyone?

They're my go-to summertime wear.  I've developed my own top pattern, both with and without a side bust dart, and frequently tinker with it to make the end product more interesting.  Like cutting on the bias, or adding pleats, for example.  I've also experimented with overlapping:

 and layering, here with shoulder pleats:

So when I saw this Vionnet top: 

CD$806 - ouch!

I thought, hmm, that's an interesting variation - and then, could I make it?  Drafting the front panel piece and attaching two of them to an ordinary back pattern piece seems simple enough, right?  It would be, but that's only half the story.  Look at the unusual seaming going on at the back: 

It has really interesting implications for the top's construction. Those shoulder yokes, for example?  I'm guessing they're not just decorative but functional too, that each is a continuous extension of the front panel, with no shoulder seam.  The diagonal seam from the armscye to the waist may also be an extension of the front panel around to the back:  which would imply that there's no side seam either.  Those were the two assumptions I went with.  

I started with a little schematic and sketched the one-shoulder diagonal panel:

Then cut out two of them. Voila! the front:

Starting with the same top schematic I sketched in the back seam lines, straightening the lines of the armscye a little for that futuristic aesthetic:  

The CB seam is useful if a sway back adjustment is desired, which is hinted at in the above layout.

Laying the front and back pieces on top of each other, the pattern pieces do look as they should - a tank top.

But when they're rearranged - combining the upper back shoulder yoke and lower back peplum pieces with the front panel, the pattern pieces look pretty extraordinary: 

Two pieces of each are required for the top; the CB seam would be at right in the above pic.  You wouldn't think you could possibly sew together something so odd and make a little top out of it, would you?  

My first proof of concept pattern pieces looked a little more complex:

Look at that:  I created a monster a rooster!!!  But it was drawn exactly on my TNT tank top, so I thought, OK, let's see how this works... And... it does!

The SA's are unfinished in the above, so it's pretty close round the neck and under the arms, and (thanks to a tiny drafting error on my part) it needs a bit more room round the hips to make those front panels more floaty.  The eagle-eyed amongst you  may notice that the shoulder "straps" are of different widths: I added a sliver of fabric to the left shoulder to round out that odd corner created at the shoulder seam point, where the outside front and back pieces met.  And it's also notable that this design demands a bra with straps that are set closer to centre than what I'm wearing. Peekage is not a look I favour (yuck!), and I wouldn't actually wear this design until I found a suitable undergarment.

The back is very close to the original.  The shoulder yokes could should be decreased in width and shortened vertically, and the diagonal peplum seam raised a bit. One important functional difference is that the original has a CB invisible zipper, but my top doesn't.  When you try to pull it on with both arms, the neckline closes up - a function of those loosely hanging overlapping panels.  So getting into it is a funny sequence: first the right arm, then the head, then the left arm, then you shimmy the whole thing down.  The zipper is truly unnecessary. 

More to come, after I've worked through these revisions.