5.1 System Front Speaker Separation B&W 802D

I am moving into a new house in August and need some guidance on speakers separation. The room is 18' x 16' (5.5m x 4.9m), Front L/R speakers will be on the 18' wall. I intend to install all the speaker cabling in the wall out of sight. What is a good starting point (speaker separation) for the front B&W 802D speakers? I realize ultimately trial and error will optimize the speaker positioning, I am just looking for a good starting point for the speaker cables to come out from behind wall.

The rest of the system is all B&W; HTM2D center, N805 rear surround L/R and ASW850 sub. Power amp is a McIntosh MC207 (7x200W), I intend to bi-amp the front L/R speakers so I can use all 7 channels of the MC207.

Thanks in advance for your help/guidance.

Marcus