What is the allowed transit orb?

The general assumption is 5-10 degrees for planetary influence. However, one degree is used as transit effectiveness at astro.com. The closer the orb, of course, the more the influence. I would think it is exponential, that is, like gravity and radiation, as the distance increases, the strength decreases with the square of the distance. So with that as a guide, I would think that one degree orb is 64 times as strong as eight degrees, or, conversely, 8 degrees is 1/64 as strong as on degree.