Gee, I think I said that a long time ago that a wider the belt would lose low end. Anyway, I just bought one too so when I get it on I'll see what happens to mine. I'm already geared pretty darn tall with the 16" rear wheel, so I may not be able to handle it.
You've (we) changed the actual low gear ratio with this belt because it isn't allowing the belt to drop all the way down into the bottom of the variator (land locked). There's nothing you can do short of adding a spacer to move the outer plate out enough to allow the belt to seat on the shaft. But then you lose the advantage of the wider belt on the top end of the pulley that gave you more speed being too narrow. Although, you will still have a better, stronger and longer wearing belt.
Try adding an appropriate sized washer or two to space the plate out a bit and see what happens.
You can try to go a little bit heavier on the variator weights to help compensate by giving it more tractability on the low end like a Stock Express.