I just checked on our standard BMW 540 V8 and the O2 sensors for pre and post cat are at 9 oclock (one side only ) . Had the car 10 years and never had a code come up for an O2 sensor. HTH's.
my caravan has the post-cat sensor at almost 9 o'clock. it's got the factory pipe on it, so it works alright where it's at. the "bus" has almost 175k on it now, and never a problem.
) . Had the car 10 years and never had a code come up for an O2 sensor. HTH's. 
