Okay, I'm mystified.
Last night when I posted this up, the set-up performed as advertised ... tonight I can't keep her on the track

!
Either I was in the groove previously and off the boil now or something is amiss in the game. I've noticed before that a set-up can seem to vary from game-start to game-start, so it may be plausible but the difference with this is extreme.
Also, rear tyre wear is much worse than I estimated. Two laps of the 'Ring is not really possible at race-pace. Drop the compounds to R2's, at least on the rear but be aware of what that will do to the handling.