Do you live on post or in the immediate area? If so, I assume that is why yours is the same.
When I got paid BAH it was never for exactly where my home actually was, but what region it was in. For example, my home was 15 miles outside of a large city, so instead of the BAH rate being calculated by the small 400 person population I was living in, it was based off the larger city nearby. I am no expert on any of this by no means, but I am just going off of my experiences.