As a German I totally agree with this list of beautiful small/mid size cities. I would like to add Ulm to the list as well.

Germans can have very different mentalities depending on the federal state you are in. So maybe try bavaria and but also something in the very north.

Avoid Berlin at all cost since it’s not representative for Germany at all.

I know you prefer cities but I have to say that I am from a small village and there you will find the most German Germans in existence.