I don't know if this will help. In TT at Silverstone I just could not beat my own ghost. Not improving at all, no matter how I fiddled with the setup for the car. I noticed an online friend had posted 1.4.xx secs faster than me using the default setup and like me no assists.
So I raced his ghost, used the default setup and waited to see where I was losing time compared to him, figuring it was probably the way I was taking some turns that accounted for my loss of time, rather than my setup.
To my surprise, I was about 1.2 secs ahead of him all the way up to the Brooklands, Luffield Woodcote corner. From then on I was at least 1.2 secs behind him.
After about 10 minutes changing my approach to that turn, and then a slight adjustment to front toe, I immediately gained 0.8.xx secs. So now I can see where else I can gain. So my tip is, pick a ghost over a second faster than you and using the default setup. At least then you will know which parts of your lap can be improved by your approach, rather than the setup.