Thanks David.  Also saw this, not real scientific, but assume pretty directionally correct and easy to do:

Before you start with the exercises, let’s first figure out the
extent of your thoracic immobility. The industry standardized way of
determination is a simple one:

1. Lie down on the floor, back flat against it.
2. Your knees should be up with your feet and glutes flat on the floor.
3. Lock your elbows and bring your arms directly overhead, attempting to touch your wrists to the ground above your head.
4. Make sure to maintain contact between your lower back and the floor; don’t arch your back to get your hands in place.

If you can’t get into this position
and touch your wrists to the ground, you have poor thoracic mobility.
If you really had to struggle through discomfort or even pain (don’t
fight through pain!), you have less than ideal thoracic mobility. And if
you were able to breeze through this drill, you should probably still
work on more mobility, just to shore up what you already possess.