So…update: I tried both sizes on again. I put on the S and did plenty of movement testing, and it feels fine. I’m a little more *aware* of the shoulder in it, but it does not feel tight or pulling or uncomfortable. It passes the reach and hug test better than other tops I own!
I tried on both for my husband. He much prefers the smaller size.
He says the larger one just looks big all around, and he sees no issues with the shoulder in the smaller one. He said the rear view of the M was just way too much fabric, even the length was a bit overwhelming. And the neckline is super low in the M. He also commented that the sleeves look too wide in the M as well.
So, the small it is! Thank you for all the feedback. I’m packing the larger one up to return. Now I just can’t wait for cooler weather to wear this!