I know the answer is tempting to be "cram them in there as tight as possible with backboxes touching". But realistically how much space do you tend to put between your games. I mean you need to work on them, etc. im a big guy so i had some extra space in there... But now ive got 3 machines in a room where 2 are comfy, and 3 will be tight. Just trying to figure out a balpark spacing. In prep for getting the 3rd machine moved in, i put them about an inch apart and man that just seems too close. And reaching the playfield for wiping down etc will be impossible.