So, you know how (in 2009) you can specify the thickness of a drafted rib at the wall interface?  I always figured it found the thickest portion of the rib after the draft was applied and set that to the inputted thickness value…  That’s not how it works though!  It’s actually dependant on the sketch line that it’s created from.  So now, if your rib is going to extend into multiple flat surfaces, it DOES matter where you place the endpoints of your rib’s sketch lines!  To specify the surface that the rib’s thickness value will be applied to, you need to sketch your line so that it does not extend past the boundaries of that particular surface.  Check out the images below…

…The first sketched line will produce unpredictable results because it passes over multiple surfaces.  The second sketch produces the 1.5mm measurement shown in the last image.