Through discussions w/ snorkel wearing X owners, I've concluded the Xtra mileage/power comes from a few things.
1-The air is cooler when coming from up off the ground at intake height.
2-Because of the snorkel opening and tube design, the air is almost "rammed" down into the filter/intake, creating a more steady,positive flow.
3-Any large plastic tube,(like Rtype stickers) will automatically add 5-10 hp.
It's in fact the next thing on my mod list.