I have the same top gap on my 2008 Bighorn. Haven't paid it any mind as the door is for privacy, not air stoppage.
My personal concern, and subject of previous postings on other threads, was the door latch/striker plate mounting. The striker plate had to be mounted on machine nuts as standoffs to make up the wide gap, the mortise cut-out on the door frame at the latch had to be enlarged, and finally, just yesterday (after owning the rig over 2 1/2 years), I figured out that the striker plate was mounted too high, not allowing the latch to go into the plate. I could not re-drill the holes because they would be too close together. I had to elongate the screw holes with a file to make it work. But finally, it works RIGHT!!!
Just another finish and fit issue that shouldn't have left the factory.