Peep ID help please

Hard as I try, I remain peep-challenged. Two peeps were foraging in a tidal cut at Sandy Hook (NJ) yesterday. This one was the larger of the two. The smaller had black legs (not yellow like a Least), and a darker head and some whitish supercilium, and lacked as much of the rufous coloring as the one shown here. My first guess is Sanderling for the one shown here, but it wasn't darting in and out of the waves on the shoreline as I expect to see Sanderlings doing; rather, it was foraging just like the other (which I'm guessing is a Semipalm). If a Sanderling, it's certainly not a male in full breeding plumage. Maybe a female, or juvenile, or transitional? Any ideas?

Hi Bill,
The plumage looks straight up Sanderling imo., though I can appreciate peep ID difficulties when they don't behave like you are used to them behaving. I think Sanderlings in breeding plumage are striking!

Looks like a Sanderling just starting to come into breeding plumage to me, Bill. The bill looks looks right and the black shoulder patch is still showing.

Thank you Shawn and Dan. It's what I suspected. I just need to develop more confidence in my peeps.