Reduced skeletal muscle tone during sleep is pretty much established. If you find out, that there remains some increased muscle tone which correlates with insomnia or reduces the efficiency of PTAS, you could target it. Though you're already targeting it indirectly via delta waves.

Yes, reduced muscle tone is absolutely established, now I think I know what you're saying. We're often letting the researchers guide the areas they are most interested in. Lot's of interest in Alzheimer's, Parkinson's, and depression. We're interested in looking at insulin response and other metabolic factors.

Yea, lot's of interest in making the subjects better taxpayers rather than how the brain/mind actually work.

Insulin response and other metabolic factors seem currently not measurable non-invasively, like EEG. That's why I was focusing on muscle tone as an easily available parameter which can be measured continuously and non-invasively, in line with EEG. Temperature is another similar parameter and I've seen a couple of studies showing reduced frontal lobes' temperature promotes sleep.

It can seem tricky to reduce it without pharma or techniques performed while awake, but I've collected a corpus of research which may allow to emulate the action of e.g. GABA without adding the actual GABA (which is thought to induce muscle paralysis in sleep), thus non-invasively promoting the reduction of skeletal muscle tone.