Roon uses R128… dr.loudness-wars.info uses Crest Factor Dynamic Range.
Crest Factor Dynamic Range measures the difference between the average loudness and the peak loudness.
R128 DR measures the difference between the 10th percentile and the 95 percentile of loudness.
Basically, Crest Factor is average to peak, R128 is bottom to top.
However, R128 ignores the very extremes, so small amounts of loudness and small amounts of silence are not allowed to alter the measurement.
More info here: https://wiki.jriver.com/index.php/Dynamic_Range