They do run much slimmer than standard Barbours. I was at the Barbour store yesterday and picked up a Birch which is from their Dept. B line. I normally wear a size 38 Bedale and a Liddesdale in S is still loose on me. I ended up picking the Birch in my normal clothing size M and it's very fitted. The saleswoman said that's how this jacket is meant to fit - almost like a blazer. She also said the fit is very hit or miss and depends on your body type. With the Commander jacket, you'd have to size up even more so in my case I'd be an L.
Dept. B in my experience is even more fitted than To Ki To was. It depends on the piece and it's slight, but noticeable. Bragh was one such example while the Shoredace was just like last year. This is mainly at the armhole, which tends to be too high, and in the shoulder area.