Fitting the Cappuccino Dress

Hi! So, the Cappuccino pattern is the first pattern I bought from Oliver and S/ Liesl and Co, and I have yet to actually make it! I’ve tried a few times over the years; I made a couple muslins shortly after I bought it; the first, I made one out of some leftover cheap rayon and overestimated my abilities to follow directions like those for the neckband and it was terrible, which is okay. The second I was able to sew correctly, but I wasn’t thrilled with the fit. I made a 12 and the neckband was too gapey for my taste, and most of my measurements put me in the 10 range anyway. So I tried a 10 and the neckband fit well but it was too tight across my bust (I’m a D cup). So I let other projects get in the way… BUT I have been determined to make one, so I pulled out my pattern a couple months ago and attempted an FBA on a size 10. I was surprised that it fixed the spreading of the gathers across my bust, but it still pulled directly next to where the gathers meet the neckband, so instead of attempting to figure out how to add more, I decided to make another muslin, and use the 12 pattern pieces and the 10 neckband. I cut the back piece on the fold, and added a pleat at center back so that the neckband would fit the dress. I was so pleased that it fixed a lot of the issues I’ve had: the neckband fits great, and the gathers don’t pull across my bust. Victory! But, I noticed there are still these drag lines (see attached picture), so here's the questions I've been getting to. I’m assuming they’re due to the kimono-style sleeve, maybe? Is there a fix, or are they not as noticeable as I think they are? Is it a fit issue, or the way the pattern is meant to fit, and will be less noticeable in a fabric with more drape than cheap muslin? I’m sure I’m over scrutinizing, but that’s what muslins are for, right? Thanks for any thoughts and opinions!