They suggest to either do 10 stops 100-0kph or to do 3 track laps in which braking normally but from 80% top speed and then let cool down. I did both (well the first one a bit modified, as I don't know where I could do that without getting in an accidentI assume you did proper burnishing and bed in before going on track. If not, even minor undulations on the disk could create localized hot spots and maybe result in brakedown of the compound? Maybe this could explain the excess deposits but soft pedal is strange indeed.
Could be, but pretty sure the fluid is ok, it was freshly flushed and I use RBF 660, never seen any bubbles except after an entire year or one particular occasion in which the bleeding nipple was slightly leakingMy only theory here would be much better heat transmission through the backing plate heating the single piston more effectively resulting in overheating the brake fluid.
Like this one? https://www.project-mu.co.jp/en/products/other_shim.html Seems a great idea, let us know if you find something that fitsI am thinking of getting some anti noise backing pads sold separately by mcu or endless and use it with the pad hoping to mitigate heat transfer to the caliper through contact points.