Baseline height

[micfil01]

I'm having to draw my roofs manually, and I'm not sure how to get the roof heights exact since I don't completely understand where a baseline is located on the rafter (assuming it's on the rafter). I threw up a set of walls with a default 6:12 roof and got the following:

Wall height - 97 1/8"
Baseline height - 101 1/2"
Fascia top - 92 1/2"
Birdsmouth - 1 3/4"

The baseline was automatically placed on the outside of the exterior wall framing (not the outside of the sheathing/cladding). Is the baseline measured to the top of the rafter directly above the baseline? So it would vary with the pitch of the roof and depth of the birdsmouth? What is the right way to think about this - should I just set the baselines to 4 3/8" above the top-plate height of my walls since I'm using 6:12 roofs everywhere?