That's a great wah tone. I wonder if Al was using the same setup for the version of "The Clarity" off Live at Third Man? Although that sound could be a phaser as well, since I've seen a Mutron Biphase on his board.
The last time I saw Sleep, whatever envelope he was using wasn't dialed in properly. I could hear it open the whole time in the Dragonaut solo, rather than sweeping. XD is similarly hard to dial in-the line between massive sweep and no sweep at all is tough to find sometimes, at least with my rig.