To be clear, vacuum pressure switches were always supplied "as is", with details on how to adjust them to suit the driver's requirements in the instructions.
Please note that I have always provided support/advice during a conversion process, and should be the first port of call for any related problems. Over the years, I've resolved one or two issues but 99% of them have been unrelated to the conversion, rather to discs/pads/calipers, and in one case, duff tyres. The last one (and I'm not naming names), was a seriously 'soft' brake pedal sinking to the floor, which saw me free-issuing a new brake master cylinder. However, despite it being the cure in my mind, it failed to solve the problem. After a lot of head scratching, deep thinking and telephone conversations, it was finally revealed that the owner fitting the kit was unaware there are two bleed nipples on a Brembo front caliper. He had only been bleeding both fronts from the outboard sides, and as a result, air remained in the system, and there was in fact nothing wrong with the master cylinder. Needless to say, once discovered, this was an easy fix, and he now has decent brakes.
With reference vacuum pressure, my own preference is 17 - 18" Hg, but I am running the full PNM upgrades on my S4s, 6-piston fronts, 4-piston rears, and of course there may be small variances in the gauge. As before, the driver should decide how much, or how little, assistance he needs.
It remains to say that Sparky has fitted more brake conversions than anyone else, and he's my go-to guy for a good job.