I have the Wide Touring seat on my 2003 Ultra. It has a gap but it's smaller than that. Parked, it's about 1/8", with me on it it grows to maybe 1/4". Not really noticeable unless you're looking for it. I had to go check before posting.
Have you contacted Mustang about it? They might have a few suggestions before you exchange the seat.
Thanks for the replys. I did contact Mustang, and the CS was great. It turns out that the foam is suppose to extend 3/4"-1" in front of the seat pan. My seat, the foam ends at the nose of the fiberglass pan. Mustang will pay to have it shipped back to the factory and replace it..