When all else fails, use a picture:
First let me say this is what I 'think' we're looking at here. When creating depth with models (in particular I'm relating to painting little figures, but I feel it applies to what we see here as well) a ridge will have a light center/top and a dark bottom. Whereas, a groove will have a dark center/upper section and a brighter bottom section as the light from above begins to hit it more. I feel that's reflected in the above picture. The 'deeper' areas are darker.
The two lines there relate to my idea. "Don't complain unless you have a suggestion", right?
I'm not sure how you layered/created that piece but perhaps you could fabricate some sort of hard, shaped piece to go behind it, by doing that, you can make it exactly the shape you need and then bond the inside part of your outer layer and not compromise the outer surface appearance. It'll make the piece more rigid overall though as you'll have a rigid piece running horizontally across you, removing some of the flexbility for it to curve around you.
Lastly, you could apply gentle layers of some sort of stain/paint/dye to create a similar effect and while I don't think it would stand on its own (just painting the detail on), it could still be used after an actual curving effect to give it a better appearance on the eye perhaps.
Just a few ideas, I think whatever you do with the straps will be a good choice, I hate the idea of suggesting a remake, but if you end up with a better result, at least you know how you did it before and it shouldn't take as long.
Keep up the great work, you're delving into uncharted territory right now which is truly inspiring.