While I can’t see the graph (no picture or attachment), your description of the graph matches my experience when doing TM vs. mindfulness. With TM, the session starts calm, then when I begin the mantra, the session shifts to rather wild oscillations, primarily within the “active” region. I believe that TM is meant to bring about “alpha-1” brainwaves, and I’m not sure how Muse interprets these.
An interesting product development idea would be to have a TM setting (or setting for other types of meditation) to help record progress.
For now, I am seeing this profile as mentioned above as “success” while doing TM, and I do appreciate having the Muse headset record the data and track my progress as I meditate. I’m just less focused on the calm vs. active metrics.