That's what I figured.
I have an XL jacket from Kryptek and it fits pretty well (really like the Highlander camo), though after puttiing on a long sleeve merino base layer, I can only fit one more long sleeve layer, either my heavy wool shirt or my Mont Bell down jacket, which is actually not very puffy. If I wear both it binds my arms. Not sure why they can't make the arms and cuffs bigger but I think all three brands (Kryptek, KUIU and Sitka) tend to size their stuff about the same.