Interesting. The person that did my tint also mentioned that the Charger rear windows can be challenging - although I think he said it was because of the size and shape rather than the defroster lines. He had to do it twice for mine as well, and I can still see some bubbles that haven't gone away after months. FWIW, he used ASWF brand ceramic tint.
I haven't worked with this tinter before - it was someone my detailer brought in because I wanted to have the detailing and tint done at the same time. So, I have no idea as to whether they typically do a great job or not, but my detailer agreed to make it right whenever I'm able to bring the car back in. Unfortunately, he's back home in CA, and me and the car are in NJ at the moment so it might be a while.