Maybe you could try this : go easy on the first sectors, when you come at the last sector, give it all you got, now use this ghost and improve on first sectors, you will see the third will get along...
It is normal what you experience (in my opinion) you are probably more practising on the first sectors, once you passed them with a good time, you get a bit more relaxed, what brings your time down aswell.
Something else I also am doing the last tt's, is not fixing myself on times, I just do sessions, 20-25 laps, and then i see what came out of it, then i try to improve on curves where I left time....
Then again, I am a much lower ranked player then you are, so maybe there is not to much advise to find for you in my gameplay
Edit:
Did another session still on Chris' tune. Found some improvement in the first sector.
28.780
25.029
13.921