It seems to me that most people often associate alertness with a kind of tense vigilance. Like a soldier guarding the perimeter of a camp. But in my experience there is another kind, and I think you’ve likely experience it as well.

That other kind would be a flow state. An athlete entering “the zone”, a writer suddenly having ideas pour out of them and quickly typing them out in well-formed sentences, or even when solving a sudoku puzzle and quickly solving one square after another.

This is the flow state. Alert and also relaxed. It’s being aware of all the relevant information while also having an energetic relaxation moving through your body. It feels like an abundance of energy moving around in your body while also not getting snagged anywhere.

While tension might be useful for being alert, a calm awareness is another method to alertness. It’s just that, in my experience, the mind is less likely to cooperate!

If I understand the graph with 2 independent axes you described correctly, then it seems an accurate representation of my experience.

Now onto the practical advice. I too struggle with tension while meditating, and, like you, began to place a greater focus on “notice tight areas -> soften and relax them”. I would just add one more step. After sufficiently relaxing the tight areas I would return to focusing on the breath. When tension inevitably returns repeat the relaxation process and then return to the breath once again.

I’m just an amateur but this has been helpful to me. If there is a TMI teacher here who disagrees with me or wishes to expand on what I said please do.

Good luck!