I work with historic timberframes and it has been my experience that traditional jounery is based on laying out from the "Framing Face". i.e. braces are framed 1 1/2" & 1 1/2". Tie Beams can be 2" & 2" or 3" & 3" etc. Something to that affect. Why? It was my understaning that this was simply to make the layout process systematic and it would be easy to layout using just the Blade/Tongue of a framing square.

Funny thing is laying out from the "Framing Face" could mean the master builder used one of the following layout methods. Scribing, Snap Line Square rule, Square rule or Mill Rule.

PS