So what would the ratio need to be I have two rows 4 on the top and 4 on the bottom?

I have purchased this software and absolutely love it only problem I have is spanning I don't know what offset to use I am on a Mac Pro that is hooked up to 8 43 in Samsung Monitors running 720 P what offset would I use for Top Bottom Left and Right to fill the screen I played with it but can't ...