I've had different kinds of insomnia over time, including the kind where I would just be clear-headed and awake, not at all tired, but neither wired. My body just wasn't interested in sleeping. Like you describe. I'm not sure what the cause of that is. It could still be cortisol levels. Maybe the early-wake-no-backsies insomnia is adrenaline based.
There's a kind of phase where my day-long cortisol levels are high, I feel energetic, my mood is great, I get tons of things done, but usually come grinding down a few days later with general irritability, sore joints, a weird libido spike, tendency to get cold sores, etc. I think that up phase may have been when I was prone to sleeplessness on trying to start to sleep. I don't know what's going on with my body during the up phase, why it's (as speculated) day-long high cortisol. I'm guessing it's a kind of physiological out-of-whack cortisol cycle, probably mixed with what-time-of-day-is-it? hormone cycle being out of whack.
I think my current insomnia is more limbic — I am emotionally on edge, Reviewing & Rehearsing, hyperfocused on fighting (my problems), anxious. I think my brain, whether the thoughts have risen to an intellectual level where I can see them, is jumping to fight, even before I wake up, and I think it's using adrenaline to power the more immediate battle.
So my guess is I need to calm down my emotions, and you need to get your hormones on a more regular cycle. Probably you also need to calm down your emotions. You might try melatonin to reorient your cycle. I found I was really sensitive. .25mg before bedtime and I was more frequently able to fall asleep and would have vivid, strong dreams. Maybe try taking melatonin at the same time every night whether it actually gets you falling asleep. Just to try to kick the cycle back into regularity. Now, it's better if you actually do fall asleep. That'll help your clock reset even more. Some other sleep aids that come to mind: 5-HTP (beware interaction with SSRIs), avoid stimulants, don't drink alcohol, walking in nature during the day, whole-body and engaging (making you think of nothing but what you're doing) but light physical activity (like dance or yoga). Maybe chamomile? Or Valerian?