Your outer pad is already dragging? That should not happen, are you sure?
What you are describing (sitting and standing on the brake pedal and it slowly sinks) that happens to all, even with the stock caliper. It has to do with the two step MC and the ECU power assist causing a huge increase in pressure vs pedal effort. I can't say for sure with your calipers, but I can say for certain with the Macan/Q5 caliper those mods do prevent this from happening. I explain why in the post (with a diagram). There is nothing dubious about using RPV's, they have been used in countless street and track applications for decades.
There is no other larger MC options for this car, and other than going to a different caliper (like the ST40), there does not appear to be any other way to improve it. As the original guinea pig now with thousands of hard street and track miles, it works and is perfectly safe.
The only thing I am butt hurt about is the fact that no one mentioned the brake pedal issue before I spent the time and money to upgrade to these calipers. The issue was very apparent from my first test drive, then I find that everyone noticed it but did not want to talk about it (why I still don't understand), but great thanks.
The stock system has a lot of intentional slop in it because VW is using the ECU to actuate the brakes for you. If you don't like that because it makes it difficult to modulate the brakes under track conditions you can turn off some of the ECU assist, but then you are left with a lot of unnecessary and unwanted pedal slop.
The modifications I did go a long way towards fixing that slop, and it has to do with the two step MC I show and talk about in my post. I did this to fix this issue for myself, and I did. You post telling us you are having the same issue and I am just trying to help. I would not describe myself as "butt hurt" just perplexed when I am the only one here who admits to having the same issue and has found a working solution.
You can learn to live with it (apparently that is what most have decided to do), or try my recommendation, or get a different caliper. The only one that reportedly does not suffer from this same issue is the ST40, and I believe it is because they have a significantly smaller piston displacement (almost 25% smaller). I bet that also keeps the MC in stage one, that combined with the smaller MC/caliper ratio I am sure give a very high and firm brake pedal. If I was going to spend $3-4K on a brake upgrade, that is the one I would get.
This is supposed to be just for fun, and arguing with arm chair engineers is not my idea of fun, so good luck.
There are so many fallacies with your initial posts and questionable data collection methods, I don't even know where to begin. Instead of belittling everyone and calling them 'arm chair engineers', how about we get back to facts, and not conjecture?
You regularly use 'belief', 'bet', 'suspect' and a whole host of words that essentially translate to 'I think this is correct, therefore it must be how I put it'. Or simply, assumptions.
1) The VW M/C isn't a stepped bore design. If it was a stepped bore design, you would see two DIFFERENT piston diameters listed. Instead, what we have is ONE diameter listed - 23.81mm. (refer to: https://www.abs-bv.fr/pdp/61546 ). Not only that, the diagram you referenced shows a step bore FOR THE REAR CALIPERS. Step bores are used mainly to compensate for rear brakes that need large fluid movement (aka drum brakes). Shitty diagram of the MK7 system below (P/N 5 & 6 are the hardlines to the rear of the vehicle):
2) Your conclusions come from test methods that are flawed. Let's start with your piston retraction testing setup. The normal procedure is to hook up a dial indicator (positioning it such that at rest the indicator is reading greater than zero) and apply minimal pressure (only enough to move the piston until the seal deforms and no more) then let off the pressure. You elected to A) use a deformable aluminum C channel (with laughable wood spacers to 'center' the block), and B) used feeler gauges. You didn't bother listing how many trials were performed and if there was any averaging employed, but yet expect everyone to believe on blind faith?
3) You didn't bother repeating your lubrication efficacy test. Once you discovered RRG 'gave' you a retraction value better than OEM, you just left it at that. How old was the OEM grease? Because the RRG was definitely newly applied.
4) The 'objective' test images are ambiguous. Just how are you even gauging the activation point? The pictures show you applying the brakes, BY HAND. Unless there is gauges and numbers backing up the application force, plus how much the pistons come out, this is not objective at all. I can manipulate those images in seconds, it proves nothing.
While the effort was laudable, there are simply too many areas where gut feeling (subjective-ness) was substituted for objective results, not to mention the misleading title of the thread. Low pedal? Sure, you don't have to press as much to get the pads to contact the rotor. Soft? Nope. The core of your modifications revolve around a check valve which maintain a small amount of line pressure at the caliper thus reducing the distance between the pads and rotors to effectively nil (that isn't even taking into account of pad taper, which is perfectly normal in ANY system). This doesn't result in a 'harder' or 'softer' pedal - check valves are designed such that there is minimal frictional losses one way (via spring rate for the plunger/ball). In other words, the RPV would have minimal effect on pedal 'feel'. Pedal position yes, but feel? Use some logic here.