The compromise proposals were all generally constitutional amendment issues. Tariffs were a legislative issue, and when the Morrill tariff went up for debate the southern senators tried repeatedly to amend it. Their amendments were shot down one after another.
Thomas Letcher detailed 6 conditions that had to be met to avoid Virginia secession.
Yeah, and Sen. Robert Hunter of Virginia cited the Morrill tariff as an example to history of what the North would do to the South when it alone controlled the government. It would therefore seem that these two men differed on their conditions for their home state. It would also seem that Mason, who was a chief backer of Hunter during the tariff debate, shared in Hunter's position about Virginia.
If tariffs were the major sticking point then why didn't the southern senators address them?
They did. Robert Hunter of Virginia spoke for 7 pages in the congressional record in one speech alone against the tariff. James Mason of Virginia, Robert Johnson of Arkansas, and Thomas Clingman and Thomas Bragg of North Carolina backed Hunter repeatedly in the Senate. Louis Wigfall of Texas denounced it while speaking in favor of secession before the Senate. Robert Toombs of Georgia denounced it back in his home state while making the case for secession there.