After consultation with Ranga on the subject, it was concluded that the NAT Traversal configuration panel currently shows two configuration elements that can be removed for simplicity:

External Address: can be removed completely from the configuration panel. The corresponding <mediarelayexternaladdress> information element in nattraversalrules.xml generated by sipXconfig can also be removed

Local Address: can be removed completely from the configuration panel however the corresponding <mediarelaynativeaddress> information element in nattraversalrules.xml generated by sipXconfig must be kept and initialized to carry the IP address of the sipXecs box.

BTW, the nattraversalrules.xml now has an accompanying XML schema file. Please be sure to also modify sipXproxy/meta/nattravbersalrules.xsd accordingly.