Oranges and apples, maybe - I don't have a TT, digital only, I have a cheap media table I used as a rack, thought the tube amp was already well isolated, but my results were like yours, great improvement when I removed the table and put things on the floor, and I haven't even cleaned up the cable runs yet. I think gobsmacked is the technical term for my reaction. I was so surprised I went back and forth a few times to make sure, which was a bit of a pain, but hey we like to suffer for this hobby.
Would a good A:B test be to move the rack to a sidewall, maybe that would determine if it's isolation or reflection that's the culprit? Might provide direction for next steps.