The secondary service area of most Class I-A stations, such as WFAN, was
limited to the local noise floor, until some of these stations were broken down
by the clear channel decision in the 1960s (affected 13 of the Eastern U.S.
Class I-A stations, and none of the remaning U.S. Class I-A clears), and until
the "Rio" treaty (affected the remaining Class I-A clears, of whatever
country).

After the clear channel decision, the secondary service area of those affected
Class I-A clears was about 1,500 miles, or more.

After "Rio", is was about 1,000 miles.

Now, it is much less, sometimes no more than 700 miles at best, and perhaps
much, much less at worst.