I am not surprised, if you look at my post doing the RPV's alone only gave a slight improvement. It wasn't until I greased the seals with the RPV's installed that I got a big improvement where now the pedal does not go soft with the engine running. It is about keeping the MC in stage 1, doing both is what gets you there. Doing each separately provides only a slight improvement, sorry I thought I made that clear, but perhaps not.Today I drove a friend's 19 Rabbit Edition with the stock PP brakes. With the red rubber grease and bleeding in the VW order, then going back and doing 29psi simultaneously bleeding the fronts, mine felt about the same.
Once the MC piston travels past a certain point it goes to stage 2 and drastically changes the MC/caliper displacement ratio. See below, that is what causes the pedal to soften, see image below. The lube or the RPV alone reduce the gap between the pad and rotor which helps a little but the MC still moves into stage 2, it is when you do both and you reduce the pad/rotor gap even further that prevents the MC from moving into stage 2 and you get a much firmer and higher pedal with significantly better feel. You have to use more muscle but in a good way for threshold braking. Make sense?
If you recall when I had the RPV's at the MC it felt awesome but I was getting drag at the rear, then I put the RPV's in the wheel well and it helped but I was not exactly thrilled after feeling what it was like with the RPV's at the MC. Then when I greased the seals with the RPV's that is when it gave the results I was looking for, not quite as good as having the RPV's at the MC but still a huge improvement where the pedal does not go soft with the engine vacuum assist on.
I showed you all pedal measurements, but that is only half the story, I can't really demonstrate the improved feel, but I am telling you...
If you look at my test data the grease and the RPV's separately each give similar reduction in piston retraction. Do both then tell me what you think.
Post reference: Post #6 How to fix/improve low soft Brake pedal with Residual Pressure Valves and seal lube
.0005" doesn't seem like much but trust me...
As for the stock single piston caliper I found very similar results:
I am fairly certain you will get the same results with the stock calipers. The main difference with the stock calipers is they have no piston coating, which is why the OEM requires seal lube. Out of curiosity I tested them with no lube just brake fluid on the seal and the retraction jumped to .024" you definitely don't want that, I bet the pedal would almost be to the floor.