This question came up in the Online 10-day Retreat Nov 3, 2020, guided by Delson Armstrong. Day 0 was part of a daily 30-minute discussion on the suttas, the Dhamma talk and reflections.
(Slightly edited to improve readability)
No, you don’t want to look for any kind of tension in the body.
Earlier somebody asked a question about doing the Relax step, but not necessarily finding any tension in the body. That’s fine, you don’t need to. The Relax step is not only letting go of the craving in the form of that tension, another aspect is that it’s also tranquilizing the bodily Formations. It’s something that is mentioned in the Anapanasati Sutta (Majjhima Nikaya 118); whenever you breathe in or out, you tranquilize the bodily Formation. This tranquilizing is the deeper effect of that Relax step.
If you are aware of tension and see that it’s there, you intend the Relax step to let go of that tension, which is that Craving.
Even if the tension is not there, utilizing the Relax step whenever you get distracted, will release Formations, will let go and relax the Formations, no matter how subtle they are.