I hope you get a reply! I can't stand the main engineering on my Defiant retrofit. It couldn't possibly fit in the ship unless the Federation developed TARDIS technology. And where are the consoles that are supposed to be on either side of the captain's chair?
As seen in STO, the Defiant's engineering room could not possibly fit in the ship and is seemingly several decks away as a turbo lift is required to access it.
As seen on screen in Star Trek: Deep Space Nine, the engine rooms of U.S.S. Defiant, U.S.S. Valiant, and U.S.S. Sao Paulo were only two decks high, were on decks one and two, and it doesn't take a turbo lift to get to from the bridge. It should be just down the hall...
Speaking of halls, why are the corridors so massive in the STO Defiant interiors?
The corridors aboard Defiant should be much smaller. Like Riker says, it's a "little ship".
So, Deck One should have the bridge, transporter room, and access to main engineering.