Derek,
It's a real joy to see the progress on your chairs.
When I had to make a similar angled back to arm joint, I ended up using several 1/8" x 2" splines. I was afraid to even attempt the tapered finger joints as you did on your Wegner chair reproduction.
I wonder if splines between the arm to leg joint with similar wood as you used for the tenon wedges would work well.
Look forward to seeing more.
Regards,
Jeff