It'd be just as confusing with a one piece, I think.
Here's how I did it on my harp uke... cut the scarf piece extra thick so you have plenty of wiggle room. Once you get it glued on, plane the headplate gluing surface at an angle, until the transition from fingerboard glue surface to headplate glue surface matches the angle of the nut end of the fingerboard. The exact headstock tilt-back angle isn't critical, so as long as it looks about right you should be fine.
Then chisel the back of the headstock until it's consistent thickness, and voila
There's probably a more mathematical way to approach it, tilting the saw when cutting the scarf joint in the first place, but I'll have to do a few more to get a better mental image of the geometry.
