WBZ is one of the two Class I-A clear channel stations with a directional antenna, the other being 870 WWL New Orleans. They weren't required to have a DA but they did it to put a better signal over their population centers. In WBZ's case, it goes west from Hull, Massachusetts.
So that might be why WBZ gets picked up in places like Texas easier than the other Northeast non-directional clear channel stations (660, 770, 810, 880, 1180 and 1210).
In 1968, as the FCC reduced protections for clear channel stations, KTWO Casper was given permission to move to 1030 at 50,000 watts, directional at night to null away from Boston. Before then, in the 50 states and Canada, there was nobody on 1030 at night. Only a daytimer in Corpus Christi. Puerto Rico has a 10,000 watt station on 1030 and Mexico City has a station running 5,000 watts at night.