Yeah man, you'd think I could go wider. I also ride a 155; '11 NeverSummer Evo w/ Union Contacts on it. I've got it as wide as I can with still keeping the regular 4 bolt pattern. I could cram them out for an extra inch by putting the bolts right next to each other. I'm not sure if that makes sense- I can post pics when I have the chance if you want. And the 22 inches is measuring form inside to inside of the baseplate. Inside to inside of the binding's edge is even shorter, of course. And, for being 6', I don't think the board's that small on me; I had an artifact (156) set up with about a 24 inch stance, which I liked. If I were to pick up something like the Heritage, size-wise I'd probably go with a 158. I'm basing this off of height, weight, and shoe size. Does my size seem about right for the Evo? I've been riding that size a while and loved it. Spins, jibs, butters and flips.
155 is fine for you, you could even go shorter if you wanted. But ya it makes more sense now that we know how you were measuring