So The port stuffing made an obvious improvement in the response. Another view of the change is rate of decay. According to the psychoacoustic studies, the Cumulative Spectral Decay plot, or CSD, does not display the more audible delayed outputs. A Spectrogram would be more relevant. The top 2 graphs on the left are of the 90 degree off axis plots and the bottom 2 are on axis. You can see the cotton make the decay slightly faster but since the first reflection point of the graphs with cotton is sooner, there is a bit more noise late in the graph which contaminates the results. That can be reduced by graph manipulations, but left in for demonstration. Basically these don't tell us anything other than what the Frequency/Impulse Response tells us.
They just shed a different light on the situation.