speaker placement 7.1

[aussiepete]

i currently have 5.1 speaker system but have purchased onkyo sr605 7.1 system im using jbl ceiling mounted for the rears i now have four of them room size is 6.2 meteres long and 3.6 metres wide im pretty sure the surround backs go rirght on the back wall but not sure how far apart and surround left and right line up wiht the front two but not sure how far foward they position of the back wall any help woul d be great thankyou