HI D, I have set up a few of these planes. Never with a YS though. Never used any down thrust. (0 degrees) Between 1.5 and 2.25 degrees of right thrust. I think by the looks of it, you might try using 2 washers, not 3.
I set the fuel tank as close to the CG as I could. Always kept the battery as far back as poss.
I also had never used a CG beyond 6.5" from the LE. @ the root.
This plane should do almost anything!! You are not getting the performance out of her. If the incidence are correct in the wings, must be in the set up some where?
Lets see if we can find her limits! Let me know. Good luck.