don't take advice from me...
I'm not a chassis engineer, there are plenty of those that have chimed in here, but it seems to me two big factors to be considered are:
1. What compound of the tire used? Are you actually getting them up to operating temp?
2. How much experience does the driver have in gaining the max out of the package?
Again, i am not an expert by any means, but it seems to me starting off soft to slow up transition times from straights, to braking, to cornering, makes sense?
I have no idea how the front/rear wing angles affect all this, so maybe start with a lot of downforce and trim it out as you get more comfortable?
What a fun problem to solve!!!
Kip