Flexing a Flex Plate?

The high quality washers mentioned by Hughes would only add mass to the rotating weight but being at the four equally spaced converter bolts wouldn't affect balance. Never use lock washers in this location, they will spread and become projectiles at high rpm. But for one to seat and the other to not seat there has to be either fouling in the circumference or depth of the converter pilot or bore or the pads aren't at the same height. I'm suspecting a tolerance issue with the drive side of the converter, maybe even a warp from the welding. I would send it back and try another converter (probably a different brand, if the first one had a starter tooth fail, who knows what may go out in the replacement) before I shimmed it with washers.