The tricky part was where to start the cut. I cut the laminated frame up to the point where the scarf would start. I protruded that point past the front of the jig so I could get the blade right up to the side where I wanted the cut to begin. This turned out to be a mistake but I knew it would be a conservative mistake if it didn't work out. I decided to try this out on an actual frame to see if I had right.
The result didn't fit at all. I think the problem is with how I start the cut because I'm pretty sure the slope is right. I think I need to come in from the side at exactly the point where I want to start the cut rather than lining it up and eyeballing it. I also don't want to risk any more frames so I'll have to make some test pieces to make sure the scarfs will fit together perfectly with a repeatable cut. I'll mess with this tomorrow.
I guess this is where woodworking experience would come in handy. Instead I'll just fumble around until I get it right. These little things are definitely helping me understand different aspects of the tools and how they should and shouldn't be used.