Thanks, guys, for the suggestions about toning down the bass.
JP: I think you are right on the money when you posted in the Fostex Mods Link page your hypotheses about the stock white felt: Maintaining a balanced freq range, serving as a big reflex dot to provide treble, and controlling the movement of the driver diaphragm to prevent bass bloating (paraphrased).
My last 2 mods (my version based on mrspeakers Rastapants and my BMF configuration) involved removing the stock white felt. My first series of mods kept the white felt intact. The last 2 mods have SIGNIFICANTLY more bass quantity than my first mods while the bass quality is consistently very good across all 3 mods. I had to add a reflex dot to my second and third mods, I believe, because removing the white felt diminished the treble end of the frequency spectrum. I had to add felt to my second mod and Organdi to my third mod to contain (minimally) the bass slam.
If this is really what's happening, the take home message appears to be this: leave the white felt alone unless you absolutely love bass slam and can add mod components to bring back the treble response and better balance the SQ by removing bass bloat bleed-over into the mids.