Okay, I just now ran through some experiments. Set the crossover to 200Hz so that no speaker contribution would be significant in the low bass. Took my Stryke test-tone CD and played from 20Hz up. Takes about one second to cycle from 0 to 6 on Dimension, so I was able to make quick comparisons. The level of bass did in fact get somewhat lower at the lowest(0,1)settings and this effect seemed to be over by the median 3 setting, with essentially no change between 3 and 6. I then ran mid-range tones up to 1KHz(played entirely by the speakers, of course)and observed essentially the same effect of a somewhat lower level at the 0 and 1 Dimension settings.
Since DPLII works(at least primarily)by detecting phase differences indicating reflected ambience rather than direct sound, and then removing a variable proportion of the reflected sound from the front channels and steering it to the surrounds, it would seem that pure test tones, which are simply direct tones with no reflections involved, should be unaffected by the Dimension settings. Nevertheless, some volume decrease appears, both in the bass and mid-range, at the lowest settings. What if any purpose this would have is unclear, but shouldn't raise any concerns. The lowest settings aren't frequently used for ambience steering, and if when they are used the volume decrease is noticeable(isn't noticeable to me when playing actual music)then the volume control could be raised slightly.
