The only reason to use a curb strap on a snaffle is to keep the bit from pulling all the way through the horses mouth. As long as the strap doesn't go past the horses lower lip it's tight enough. The reins should NOT go between the bit and the strap. The strap will interfere with the feel of your reins and it really serves no purpose anyway.
There's nothing like the Rockies in the springtime... Nothing like the freedom in the air... And there ain't nothing better than draggin calves to the fire and there's nothing like the smell of burning hair. -Brenn Hill