There is a lot of on screen evidence to show that the defiant was actualy meant to be an 8 deck ship. The map in the turbolifts shows 8 decks. The window configuration hinted at something much larger than 4 or 5 decks and flying along side a Miranda class, the defiant certainly looked big enough for 8 decks.
So, here is what an 8 deck defiant MSD might look like. Extra large as a christmas treat to anyone watching.