How much chance is there still habituating to it some 20 months after worsening? It's still very tough going these days...The most prominent part of my tinnitus is in that upper range. It cuts through pretty much everything because of how high it is.
The best tip I can give you is to live your life and pretend it doesn't exist. Don't ignore it because that requires effort and attention. Do nothing. It will drive you mad but you just have to not react to it. Let it be there and go about your day.
To help this along, try to keep your mind occupied and don't allow yourself to have opportunities to sit monitoring it. This could be by starting a new hobby that requires deep concentration, or by being active and hands-on with something.
I started playing more chess, and the more challenging the games got, the more my mind would wander and get lost in the tactics. I used to do this when I had problems with my chest as well - long story.
With that said, it mainly takes time and usually lots of it if it's pretty severe like mine. You cannot simply will it to happen, and I suppose if you constantly try to make it happen, it probably won't. It's a complicated condition.
Whatever you do, do not make it the centre of your life.
Correct me if I'm wrong but it seems like you're habituated pretty well, and it doesn't make a difference in your day-to-day life. If only I could get to that point.
Could it be the volume? I feel like mine's really bad. Hear it everywhere. When I think about it, I can even hear it in the shower it seems. It just makes me feel habituation to this monster is impossible.