I have no idea.
DB fields with extents are heresy. That you can create them at all is an "unfortunate" state of affairs.
My advice is to stop whatever it is that you are doing, back slowly away from the keyboard, keeping your hands in full view and your fingers far from the keys, and take a nice long walk to rethink your design. (You are probably going to tell me that someone else did it a long time ago and that you're just a poor hapless schmoe stuck with the thankless task of having to maintain this travesty...)