So I believe the problem here is that Kanger was always infamous for consistency. However, despite the differences in chimney lengths, all the tanks fit the Kanger coils & RBA properly.
The problem comes when trying to fit/use a coil head that wasn't designed for the tank. That's when the inconsistencies become apparent (otherwise I'd have never noticed them).
Exactly right. I know that my STM is authentic. I found the thread which discussed using Aspire coils (off label
Anyway, per this post, the problem was not the chimney length but diameter.