The only thing to keep in mind is the ACI of the nearby AP will partially mask what the AM can hear. So if the AP is on channel 6, the AM will be subjected to ACI in the ch 4-5-7-8 range such that it won't be able to 'hear' as well as if it were separated over a larger distance. Additionally, if the AM does containment on a bad agent, it could interfere with the AP, regardless of channel, if they are too close. But we commonly have customers deploy them side by side to save cabling costs. At least get a couple feet or meters between them.