It is frequently good to go back and re-read some threads. It is often easy to get too caught up in the discussion and lose the ability to communicate well toward the questions being asked. I will never claim to be a great communicator. I am certainly more anti-social than social. However in this thread the question was asked: How can something be less than nothing in reference to the 30 foot minimum on filter strips.
The answer is based in behavior. We have to realize that the behavior of adult birds seasoned by experience that we interact with during the season is quite different that the behavior of an incubating hen. The predator/prey conflict here is important because it occurs exactly when the hens are most susceptible. Having just depleted her own energy reserves to create 12-16 eggs, the hen now is genetically programmed to incubate. Her instincts tell her to stay on the eggs for 23 days. This instinct makes her exceptionally susceptible to nest predators. The math/science comes together somewhere near the 30 foot habitat width where the probability that the predator will find and be able to kill the incubating hen is extremely high. Anything less than 30 feet swings the adaptive advantage to the predator. Anything more than 30 feet swings that advantage the other direction. We have to understand that this is the average and differs with each hen, predator, or situation.
It is important to realize that a cover less than 30 feet can hold and sustain fall populations of upland game birds. However, we also need to understand that the same habitat can be a death trap for incubating hens. It's no different than what you can do as a single hunter in similar habitat. If it is 30 feet wide, you will be quite capable of being successful most of the time on bird encounters IF your shooting isn't the variable. In a 1200 foot strip of cover, how many birds will you not encounter??? It's this same "probability" that is at work in the narrower strips to give the birds the disadvantage. The hen is programmed to sit, weak, and essentially cornered by adaptation to incubate.