FITTING: By Hand London 'Anna' muslin/toile, adjustments for my erect shoulders (part 2).

Huh??? What is an erect shoulder??? I googled to find out more in order to accurately diagnose my sewing issue, and the results page was mortifying to view.
Advice: don't google the words "erect" and "back" in the same sentence.

Thank you to every one on Twitter and those that commented on my last blog post with advice. Without you guys I'd either throw out the Anna and give up on sewing completely or I'd hem the dress shorter at the back and live with the dipping waist seam. Every one has said that my shoulder seam sits too far back therefore causing the front bodice to ride up.

So it seems I have erect shoulders. Not sure if this is a good thing or not?? I always try to stand tall with my shoulders back. The trainers at my gym have drilled into my head the importance of standing tall ("chest out, butt out, sternum *something-something*") so I guess this is proof that I have alright posture?

I don't understand, if erect posture is a good thing, why don't RTW clothes and pattern companies design patterns to accommodate this? I feel like I'm being punished for having "good" posture.

I tried on a RTW dress and noticed that the shoulder seams also sit back (about 1.5cm). I pulled the seam forward to straighten the waist seam and marked on my shoulders where the seam should sit to achieve a straight waist seam.

I've taken some more photos to explain the issue. The waist seam is sitting above the yellow measuring tape. The markings on my door strongly confirm that the issue is my front bodice is riding up.

LEFT PIC: How the waist seam/dress sits naturally on my body.
RIGHT PIC: How the waist seam/dress sits after I pull the shoulder seams forward.

Hopefully you can see the shoulder seam clearly in this photo.
Pen mark on my shoulder is where seam should sit to achieve a straight waist seam.
Left shoulder seams sits 3cm back from mark.
Right shoulder sits 2cm back from mark (could be due to my right boob being the smaller one).

I should point point out that I have had this issue ever since I started sewing so I don't think it is the design of Anna. I used to assume it was because I drafted my own skirts or because I didn't have a Kim Kardashian butt. I also suspected I had a sway back.

Fitting issue:

• Shoulder seams sitting too far back - 3cm back on left shoulder, 2cm on right shoulder. Difference could be due to my right boob being smaller than the left?)

Which has resulted in:

• Waist seam/front bodice is riding up at the front
• The waist seam appearing like it's dipping/tilting towards the back (but in actual fact it's just riding up at the front, as per photos)
• Dress hem is longer at the back

How to fix:
I've been told that I simply add the 3cm on to the back shoulder seam.
But I also saw somewhere on the internet that I need to then subtract 3cm from the front shoulder seam.
There was also an "erect back tutorial" that advised to take a wedge out. Thanks for linking me to the tutorial Sew Little Time!

I'm still trying to get my head around there being such thing as "erect shoulders" so may keep pondering (aka tweeting about it, googling 'erect back', sighing every time I walk pass my sewing room). When I fully understand the logistics behind the fix I will cut out another bodice muslin.

How do I make the add length to the shoulder seams without affecting the neckline and armholes, as they fit well right now.

If anyone knows how to fix this issue, please comment :)
I'm sure after I fix this erect shoulder issue, I'll run into some more fitting issues. Oh the joys of sewing, always keeping me on my toes!