Incidentally, the BPW34 PIN diode has 25 pF capacitance at 3V reverse bias, so your simulations were spot on.
With the above schematics the Vr would be 8.45V - at that voltage (based on the datasheet) is the cap ~17pF.
Add 3pF stray.
So 2 diodes in parallel would require 30V to see the same shape.
The major issue with above schematics is the setting the comparator level is critical. Not feasible in real design. I cannot recommend that. You would never be able to set it properly. Another approach needs to be taken.