- If you are only doing IDS detection, you don't specifically need AMs. If you are doing IDS Protection, like disabling rogue access points, you need AMs, because APs serving clients cannot serve clients and do IPS at the same time effectively.
- If you put a floorplan in VisualRF, instead of setting it to APs, you can set it to Air monitors and it will tell you how many. IDS/IPS really occurs at the management frame level and by default that is 1 or 2 megs on the 2.4ghz side and 5megs on the 5ghz side. Those management frames can travel very far and be seen very far when sent at the lowest rates (300 feet or more). Air monitors are typically deployed using square footage, because Air Monitors do not send any RF traffic they only "see" that traffic, so you cannot really survey for them effectively.
If you have walls, you face the same challenges like APs where you have to decide where to put them, based on coverage. That is where VisualRF comes into play. Draw your walls, set the coverage to Air Monitors instead of APs and see how it looks on the diagram.