Your graphic of 1858 tariffs indicated that the Government collected about $47,800,000 in tariffs. Tariffs varied widely depending on what the imported item is. Just for argument sake, lets say that that dollar figure represents an average of 15% tariff on imported goods. That means that the total value of imports is somewhere around $318,000,000.
Who was buying those imports? Where were those goods going?
That question can be answered by asking "Who had the money to buy imports?"
With the Southern export value being 73% of the total, and the Northern export value being 27% of the total, it would be reasonable to assume that the Southerners were somehow paying for 73% of the imports.
Of course that's not how it actually worked. In reality the Northern congressional representation had gamed the laws to favor Northern interests at the expense of Southern interests, so New York and Washington DC were actually grabbing most of that export value.
New York was getting profits on the front end of the horse with shipping, banking, insurance, warehousing, packet shipping, etc. New York was also getting a lot of profit off of the back end of the Horse, through the same methods.
Washington DC was getting all their percentage of the Southern production off of the back end of the Horse, when European products arrived in payment for the mostly Southern produced trade.
I've read many accounts that assert New York made off with about 40% of all Southern export value, and Washington DC of course made off with whatever the tariff costs were, which were at least 15% in your example, but likely much more.