Yeah, I understand what's going on with the hitbox, it's just that for me it's the opposite. I think the blue fairy looks better aligned (though I think you should keep the shadow positioned relative to the sprite not the hitbox). Interacting with stuff indeed felt a bit off for the same reason to me.
I think for the sand, something resembling a dune-y texture would work better. Something with a wavy shape and two tones, like this perhaps?