"the agnostic position is that it is not possible to know one way or another."
I dont want to sidetrack the discussion, however, if I may ask: Is it possible to "know" if there is a tooth fairy or not" Is it possible to "know" whether there is a Santa Claus or not?
Is it possible to "know" if there are purple unicorns or not?
If the answer is "no" it is impossible to factually "know" whether said entities exist, then the agnostic position becomes intellectual nihilism: i.e. We cannot really "know" anything. Why? Because there is as much evidence (perhaps even more) for the the 3 characters I listed above as there is for a supreme deity. Equally so, there is as much evidence to suggest that ALL of the above entities were creations of the human mind, and human culture.
If the answer is "yes", it IS possible to factually "know" that these characters do not exist. Then the agnostic position is completely non-generalizable and only applicable to the question of the existence or non-existence of a "deity". In this case, "agnosticism" becomes a circumscribed "belief" system devoted specifically to the question of god, and has no practical application to any other epistomological realm.
In summary, if it is not possible to know whether or not there is a "GOD", than it is equally impossible to know about the possible existence of Leprechauns, Goblins, Bugs Bunny, Xanadu, or any other "potential" reality.