When "shopping" for an aux tower, you take what you can get.
Aux towers still require authorization from the FCC just as with primary sites.
In this town, there are these towers:
- College Station at about 100 feet HAAT (just an antenna atop a building)
- Country Station at about 300 feet HAAT
- Christian station at about 425 feet HAAT, but 10 miles out of town
- Tower with 'for rent' space - only about 150 feet HAAT
- Tower for government purposes that is already overloaded with antennas - 100 feet HAAT
Now, which should the country station try to find aux space on? Obviously not its own, obviously not the government tower, and probably not on the college station.
The Christian stick is 10 miles out of town, and the station is an A. That would be less than optimal, and might not meet FCC requirements for covering the COL.
The 'for rent' tower is the best option left. It is actually in the city limits of the COL, so it would work well -- but there is no space for FM bays above about 50 feet.
No matter what aux site they chose, if the station lost its primary tower, its coverage of the COL would be fairly limited. Most stations would have this problem, except in the (previously mentioned) case of well-planned backups, which would usually happen only in a cluster.