When I do a brace detail drawing I usually show the brace in place between the post and tie or post and plate, with all dimensions.
And I usually show all four sides of the brace and both ends as the program I use puts out the stick drawing showing all these.
I draw in the 3/8" layout line and dimension that.
I was just curious if your hypotenuse dimensions match mine?
I would think they wouldn't.
The actual surface of the timber the diagonal dimension should be shorter then my 3/8" layout line.
See what I mean by this drawing:

My point about this whole conversation is that I can't see how you can get an accurate layout using the surface, instead of the 3/8" offset layout line.
I suppose you can but, your hypotenuse is not going to be one of the standard lengths shown on the back of a framing square.
Jim Rogers