Interesting peep — Help?

[Tanner Martin]

Hey all, I'm looking for some ID help on a peep I saw at Lake Selmac yesterday. I'd forgotten my scope and the visibility was poor due to the smoke, but I briefly spotted one that — as I study it more — makes me wonder if I should be considering Semipalmated Sandpiper.

It's the peep in the back center, moving left. The size and head/breast coloration are leaning me away from Least — leg color is hard to judge in the light, but I sure don't see any yellow. I don't feel confident about evaluating the amount of rufous on the back given the lighting. However, the bill was noticeably shorter than typical of Western; and my photo shows it as being about the same length as the head (although sometimes a slightly-turned head can give the optical illusion of being much shorter). Unfortunately I seem to only have one in-focus photo — it flew in suddenly, and then I lost sight of it. 

I'd appreciate some feedback from others with more expertise with peeps — much as I love them, under poor lighting conditions like this I don't find myself very confident. Thanks in advance for any advice!

Tanner Martin (Stumped at Selmac)