Here is a start of something. I tried to use the bulge/zoom shader and get it to pinch the crevices to make the ends smaller but couldn't get it to work, so scratched that idea.
If you use the complement lines as a mask for the boundaries you could mix in with a smooth step of original dunes, just smaller with smooth step by clamping in, you could probably get smaller boundaries that smooth off with primary mask.
PF warp idea is kinda failed. Not sure what sort of influence heading would have when masking it.