Thanks for the tip!
The headphile C-pads ended up getting too boomy (on the SR-225i) once I made my mods (Vibro cup, 4-punch mod and placing a felt pad on the back of the driver). I tried adding sound-absorbing material to cut the unwanted resonances in the mahogany c-pad chamber, but it didn't make a very notable difference.
Furthermore, I was growing frustrated with the treble attenuation on the c-pad. They are very neutral, but it just wasn't the sound I wanted. Overall, the combination made the 225i a bit bland and boomy. A bad combo for my personal taste.
I switched back to the L-cush and stuffed the inside with a spare piece of DT770 pad foam (essentially the "Shack Hack" mod). The sound and comfort are absolutely wonderful now. And with the L-cush, any and all seal issues are now a thing of the past.