Strange that both sizes have the same number of stitches for the sleeves--I didn't notice that! They do increase differently, but the small size still seems large. I don't seem to have written anything down about the sleeves, so I'm not sure I can be of help. It did turn out larger overall than I had anticipated, but I think it did fit my sister ok.
As Ingrid mentioned, I'm not sure there's much you can do without messing up the way the sleeves fit into the body. It's possible that you could cast on fewer stitches but I don't know how that would work out. It would sort of pull the front and back up at the shoulder when you seamed it, I imagine. But if you did the same # of decreases the raglan part would still fit.
Well, I hope you figure it out! Are you using the recommended yarn? I really liked it--nice and cozy!