The Ohio River didn't allow access to foreign markets.
The situs of the collections had nothing to do with who paid the taxes. The purchaser of the goods paid the taxes, not the citizens of the collection point.
If the overwhelming majority of the purchasers of the goods were in the South as you claim then why didn't those goods go to Charleston or New Orleans instead of New York and Boston?
There is a good essay by historian Michael Scruggs about tariffs (”Understanding the Causes of the Uncivil War”), and especially the horrendous Morrill Tariff that lop-sidedly favored the interests of Northern manufacturers at the expense of Southern agricultural interests. The Morrill Tariff (named after of the New England industrialist who championed the tax) was proposed by, supported by, and passed in the House of Representatives by the North (which dominated the House of Representatives), as only one Southerner voted for it. The Southern members of the House recognized the Morrill Tariff for what it was: An economic death sentence on the Southern states.
If that was the reason for the Southern rebellion then why did they secede months before the tariff was passed?
I quote from Professor Scruggs’ essay: “U. S. tariff revenues already fell disproportionately on the South, accounting for 87% of the total.
Again, nonsense. Thomas F. Huertes did a study of Southern imports in the year prior to the rebellion in a paper he did for the "Journal of Economic History" analyzing how successful a confederate tariff would have been. For the year 1860 he identified $37 million in total foreign imports. That amount would represent a small fraction of total U.S. imports.
You said: “The Ohio River didn’t allow access to foreign markets.”
Foreign goods were transported via the Ohio River, the Great Lakes, Northern railroads, etc.
You said: “If the overwhelming majority of the purchasers of the goods were in the South as you claim then why didn’t those goods go to Charleston or New Orleans instead of New York and Boston?”
New York and Boston were closer for ships coming from Europe, and allowed them a quicker turnaround time for bringing goods back to the continent. The quicker the turnaround, the more profits the shipping companies could make. Besides, most of the major importers were in the North, especially New York (hence, many deliveries were made to Northern ports), and they were just middlemen or agents in the transaction. The actual consumer or purchaser of the goods “paid the freight.”
You said: “If that was the reason for the Southern rebellion then why did they secede months before the tariff was passed?”
First, the Morrill Tariff was drafted in 1860, and the Southern members of Congress did not have the votes to stop it. Thus, it was a given that the tariff would become law. It actually became law on March 2, 1861. Seven of the thirteen states or territories seceded AFTER the Morrill Tariff became law (Texas, March 2, 1861; Arizona Territories, March 23, 1861; Arkansas, May 6, 1861; North Carolina, May 20, 1861; Virginia, May 23, 1861; Tennessee, June 8, 1861; Missouri, October 31, 1861 — though the secession was not applicable to the entire state). And, five of those states seceded AFTER Lincoln called for the muster of 75,000 troops for the specific purpose of invading the South.