+1. As I started reading the OP, I was totally going to post this, but you beat me to it. I have never used a 17670 in this tube, only 18650's with a brass bar in place of the spring.
It's the tinyest bit of hassle when changing batteries (which is not very often!), because the bar floats loose, but is so worth it. And make sure you only use batteries with a wrap all the way over the negative end. I had some laptop harvest ones where the shrink wrap stops a couple of mm's short of the end, and they will short against the bar. No flames, just goofy operation, it's in the signal path, not the power path.