I used the Lotus set up for the expert challenge to do the British Lightweight races, one of which is Tsukuba. I was getting consistent times with that race, but I never managed to actually beat it (I think the best I did was 3rd).
However, going to the expert challenge, same car, same track, and it's like there's a micron layer of oil on the track or something, all my times are a second slower than they were when I did the British Lightweight event.
I'm using the Juliet tune, which took it from a squirrely little crash machine to something actually drivable. Maybe I'll give the Blackout Billy tune a try.
As for the Fiat, I can consistently get second. Maybe upping the top speed a little will help.
Haven't even tried the Subaru yet.