The Upside of Long Bonds in a Recession

If there is a recession, where's your upside in yield? Do we move from 4% to 2.5%? Is that a close to double-digit gain on your ten-year holding? I'd say you were short a lot of vol on the other side if I'm right. The thing about TLT is it has a mandate to keep your duration fixed beyond 20 years. So you don't get that natural rising tide benefit.