An excellent explanation. Some companies hide this by making changing the angle where the two metals meet making the part where they come together the hypotenuse of the angle.
I have talked to some companies that make bimetals and it is interesting how they do the over the aluminum joining. As it was explained to me by one company, they actually super cool the aluminum body so it shrinks a little and then they slide the steel ring over it. After the body warms back up it locks the ring in place. There is quite a bit of cool science that goes into putting one of these together and I would hazard to guess that a lot of math is required to get that joining point perfectly blended together.