Ty -
28% sounds like a lot of oil, even if Tom relieves the ring groove for running all castor. I've run nothing but 22% 50/50 in all my ST's for the last several years, hundreds of flights, yet to wear one out. I'd not want to contradict the engine tuners instructions, but I also would be tempted to ask him if running Sig Champion is ok.
If your 46 is a newer model, with muffler lugs, it could very well be the version with the high compression head with the huge squish band.
Throw in a .10 head shim and switch to a K&B 1L (long idle bar) plug. I'd bet your problems vanish.
EricV