I'm wondering if the Fairfield 80/20 is the brand that is supposed to be soaked first for hand quilting.
I took a class once from the woman who developed the Roxanne's line of quilting supplies (sorry, can't remember her name at the moment; her dd has carried on the line with Hawaiian quilting). Fairfield was her favorite batting, second only to silk, but she did say that it needed to be soaked first for hand quilting because of the bonding resin on the batt. She said it was a great batting for hand and machine quilting (regular domestic machine), but I can see why it wouldn't work for longarm quilting.
Maybe longarms need cotton batting to be needlepunched for stability.