Thanks for the great reponse. I will use this information with the customer.

I always recommended installing diversity antennas at a distance D such as:                D = (2k+1)L/4 where L is wavelength and k is 2, 3 or 4. Greater values for k would imply too much separation between antennas, so diversity effect decreases (both antennas must be close enough). In other words, odd multiples of quarter wavelength. I think I remember that measured distance on our old mounting brackets was actually this formula with k=2. However, on CWNA exam documentation, they simply talk about 1/4, 1/2, 1, 2, 3... wavelengths. I do not much agree on having distances even multiples of half wavelength. I hope this helps!