I don't know what it is, but I've never heard anyone use either Ah-men or A-men exclusively. It's always interchangeable. I find if I'm praying in a group, we're all more likely to say, "Ah-men," but if I'm by myself, I am more likely to say, "A-men." I can distinctly recall times that I have said "Ah-men" during my solitary prayers. Usually it's when I feel all warm and fuzzy inside, because you know how daughters are with their Daddies. Especially with their Daddy in Heaven. ^3^