100 dB from Pd turns magically to -50 dB in Reaper.
One thing is that Pd's objects related to dB add 100 -- 0 dBFS in other software is represented as 100 dB in Pd.
So you don't actually have 100 dB in Pd. Nor would you want that. Full-scale in floating point is -1 to +1. 100 dB represents an amplitude of 10 ^ (100/20) = +/-100000 (edited b/c at 6 am on a tablet, I miscounted zeros). Reaper would not be expecting that, and not handle it well.
That doesn't explain the extra 50 dB difference -- I've no idea about that.