I think that is fairly normal from the ones I've seen that suffer with it.
I bet the wailing and Nashering of teeth is fairly normal too! (see what I did there?
)
It does seem to be higher up the tank on the side stand side and possibly reflects the fuel level when parked? Although academic at this stage!
Once it's gotten into the paint it's quite advanced and I don't think there is a way back, although it's definitely worth waiting to see how it dries out.
I'm with you regarding the internal coatings. I loath them! All I would say is that if you are considering that, (which I doubt) then get it done by a professional who will guarantee their work properly.
You've probably already seen that Moco got himself an alloy tank for his S2R1000.
I think that's the only way forward if it's a keeper?