We have a requirements of lowering the wireless signal of an AP (or MX65W) to a minimum point where it only covers 4-8 square meter.
We tested changing the transmit power to 1 dbm but the signal is still strong enough to extend to 20-25 meter ! as we have an open space with no walls or anything to block the signal (we're trying to utilize the location analytics to calculate visitors / passerby ...
You could place an attenuator inline between the antenna and SMA connector on the MX65W. Keep in mind the connector on the MX is RP-SMA. But it probably won't be the best for receiving probes from the client devices you are looking to receive from.
Removing the antennas you won't receive the probes you are after.
Try turning off all SSIDs and use the radios only for reception for analytics ??
Rather than limiting the output power of the AP a better approach IMHO is to set the MINIMUM connect speed of the SSID. You configure this under:
Wireless/SSID/Edit/<scroll to the bottom>
This allows you to substantially limit the range and at the same time ensures those devices that do connect a solid and strong signal with a fast connection speed.