Got a new trick for whomever is interested.

Been dealing with frames that can receive driving rain onto knee braces. From there water travels down kneebrace and gets into post mortise.

With a 4" tenon that usually bears level in the post I have created a slope. Essentially a 3/12 pitch. 4" over level 1" up plump.

The neat part that is that the Makita mortiser's angle on the third canted setting is this exact angle. You can layout a line 1" up from bottom of mortise for guidance and plunge with Makita. 4.5mm on the ruler aligned with the bottom of mortise should get you to the right place. I plunge the rest of the mortise with Mafell.

Creates a nice plumb to slanted mortise for water extrusion, in theory that is.

Cheers.