Again, you are nuts. There was no tax on exports. The planters were not paid in British pounds. They were paid in dollars by the Cotton Factors who actually sold the crop. Those Factors moslty represented Northern banks. Your beloved slave driving planters paid little or no tax, and again I say without a doubt, you are nuts!
I am actually surprised. You did enough research to learn that much. Good for you! You might have learned that the North completely controlled the cotton trade. Because they did.
But you still don't understand economics. A tax on imports is virtually the same thing as a tax on exports. It's the same value being taxed whether it is exchanged for profit, or the profit taxed.
Same stuff.