Hi, section 31 page 2 no. 17
"A Lap/diagonal belt "effective upper anchorage" location must be at least 140mm from the longitudinal centre line of the seat (see note 14)."
knew id seen something somewhere.
I read it as only applying to normal seat belts and not harnesses but ive spaced mine accordingly as i may use some ordinary belts or harnesses.
so ive put in two top mounts per side and may put an extra one near the floor below the top mount so i can use an inertia real belt as i find harnesses a pain to use
anyway there it is
hope it helps