If that is what you think then maybe you better do some research. I have found Ratsnakes, Skunks, Brown snakes, rattlers and mice under the same piece of tin. Niches in nature are like apartments. They often bring species with different needs in close contact.
As to your question....
I definitly do not recommend keeping Copperheads on potting soil (or even using it as a substrate. Feces from the copperhead (and it's prey animals would soak into the soil so cleaning becomes more difficult).
This can result in mouth rot (from injesting the soil...and irritation from sand particles caught in the mouth) Body rot (from the neccessary moisture that the Brown would need) and other fungal diseases. The odds of a Copperhead developing a blockage from injested detrius is also increased.
On the otherhand, it is perfect for maintaing a healthy Brown snake population, partially because the very food that Brown's eat help in the cleanup. Also since Browns live in this niche in nature, they are much more resistant to possible disease from it. Ever watch a Brown eat a worm? They suck it in like spagetti. The slime from the worm acts as a lubricating agent so the soil slides off as the Brown injests the worm. This works especially well because of the Brown snake's small head.
A Brown snake on cypress mulch, aspen, or in a pinch-newspaper (which would be good for Copperheads) would suffer from dehydration and also would have a hard time of it since hunting worms would be more difficult. It is very difficult to get a fresh caught Brown to take worms out in the open (unlike a Copperhead) they are shy snakes. They need to burrow. Copperheads are much easier to get started.
Two inches of soil makes a very big difference in nature, and in a man made habitat. Understanding the difference and why is basic husbantry.
Frank
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"The luxury of not getting involved departed with the last lifeboat Skipper..."