Once you have set external antenna on 72
It works and makes no dif. no matter what you set
Don't forget all antennas have a H & V polarization, some deploy the highest gain antenna, as your case, and complain why they don't have wifi below the antenna, cause it works like a umbrella, the highest gain ones, are like a big umbrella, they start radiating i.e. at 5 mts. 15 feet, and that changes depending hight, the higher you deploy, the bigger the umbrella.

Since the antenna is only a metal component, you don't need and can't make any configuration on it. What you should do is:
1. Navigate to Wireless > Wireless Advanced > Antenna Setting and select 'External Antenna' in the drop-down list.
2. Pay attention to the position of TL-WA7210N and antenna, refer to FAQ: http://www.tp-link.com/en/faq-1044.html