A couple of things:
- The 14.4W (or 20.8W) is the worst-case consumption of the AP itself. Depending on the type and length of Ethernet cabling you use, the actual consumption per AP could be 1-2W higher. The switch would typically adjust for that when receiving the POE budget request (LLDP)
- The AP has no knowledge of the total powere budget of the switch, so it will not know if the total consumption exceeds the 195W you mention.
- I'm not sure what the behavior of the switch will be when the APs draw more than 195W. The power to one or more switch ports may get disabled?
- 195W gives you a budget of 8.125W per AP. Even with cabling losses, you'll have at least 7.5W average per AP. That may be plenty for many use-cases, but there's a risk.
- When enabled, IPM will simply kick in when the AP exceeds the available POE budget. If the POE source is an 802.3af one (15.4W at the source), it will kick in when the AP consumes over 13.5W. IPM wil be idle when consumption remains below the budget. If the source accepts the LLDP budget, IPM will never kick in.