I compared the pads of the HF2's and RS1's last night and, upon initial inspection, the RS1 pads looked deeper (from the tips that touches my head to the plastic grill covering the speakers). Upon further inspection, I noticed that the pads, indeed, are the same.
I suspected the speaker grills to be much larger on the HF2's, as it seems to actually "sit" on my outer ear, but was incorrect in this assumption. Both the RS1 and HF2 look almost identical in the diameter of the plastic speaker covering. The housing on the HF2 look to be a bit larger, causing the foam pad to stretch a bit more than that on the RS1.
All 'n' all (hell, yeah, to Earth, Wind and Fire!!!), by outward appearances, I would not expect the difference in the comfort level between these two cans. Since the HF2's are substantially weighter than the RS1's (as someone previously mentioned), I'm starting to think maybe that has something to with it also.
To me, the HF2's and RS1's sound so different; one warmer and bassier and the other lean 'n clean, add the airy GS1K to the mix and these could be someone's perfect trifecta. Maybe me.