how much front sauce are you running? since thats huge, also what front springs?
however, from that description you probably are around where you should be (i would get a 17lb spring, either the CRC red or the Speedmerchant black and figure out what you are running for fluids, its huge set up wise).
I have been told by mulitple top 12th scale drivers that you dont want to run more than 5 degrees of expo. if you run more (and this is from my expeariance) it actually makes it more twichy, since if you want to move slighlty, its really hard since when you turn its nothing, nothing, nothing, then BAM it TURNS! lol
I do not know how good of a driver you are or how fast you are, however a fast car has a lot of steering that doesnt scrub speed. You want to be able to make most corners without having to let off more than just a blip, however not everyone can drive that way, since it requires alot of concentration.
Ways to take out the twichyness:
-Old style front end
-Stiffer front springs
-more castor (which is tough with a strut front end since the castor blocks are poorly made)
-higher front ride height
-less front sauce
-less dual rate
-less tension on the center spring
-slight amount of exo (try like 3%)
-Parma Bently Speed 8 instead of Ascari body (if you are running an ascari)
Really the best suggestion I can give you (Since i dont know exactly what the car is doing, someof the time if its twichy it could be a mechincal problem, not set up issue) is to find someone at that track who is really fast and ask them for help. I can try to diagnose the problem online and give suggestions, however it only goes so far.
Hopefully I was of some help...