As Mr Simpson says, agency buyers and planners look at the delivery of AQH persons, not the delivery method. Nobody at the agency level cares the power of a station.
At some point, the heads of agency media departments learned their trade and craft. They were taught, in some form or another, that a lower power FM at high antenna elevation might be better than a high power and low antenna one. Or that an AM with 5,000 watts at 590 covers more than a 50,000 watt one at 1510.
So, if they are not already totally confused, they realize what is important is how many people listen.
That's why sales kits don't have coverage maps any more. That is why group owners sell clusters of stations in combination. That is why time buyers also look at station streams and other factors.
In fact, a lot of time buys today are done with a computer program and no sales pitch, no analysis of the morning show or whatever. Just "how many of my target listeners in the target age-gender-ethnicity-geographic area etc. does the station deliver at what cost". If the result is good, a buy is generated.
Heck, the software could even be set up to buy fewer spots on stations with higher TSL and more on stations with a low TSL. Optimization of Reach & Frequency is easy.
