I made these little test pieces to match the width of the frames I have. The method I'm using to start the cut is to line up the point on the frame where I want the scarf to begin with the front most point of the jig as shown in the picture below.
I made those dips in the side fence so I can get the clamps down a little further. I noticed this will help with getting the frames snug against the jig, closer to the cut. The distance of the fence is set so that the front-most part of the jig is millimeters from the blade (shown below). This ensures that the right side of the blade will leave a cut that starts at exactly the right point. The angle of the jig does the rest and the cut ends right where I want it to.
Next, I'll need to try this out on an actual frame, but everything looks good at this point. I'm pretty happy I finally got this to work.