Satch, sorry, my TT is mounted the same as yours -- TT shelf into conc. block wall, on constrained layer damping platform.
I've assisted with three of these mods, mine, plus another Studietto here in town, and remotely, a Studio restoration in Australia. (I have also read very favorable reports from others who happened upon this upgrade quite on their own.)
Anyway, all three of us are amazed by the results! The springs truly suck, and I'm sure if M. Lurné had access to sorbothane he would have used it ;--) BTW, we use sorbothane of three different durometers (hardnesses) providing the same effect as the three different spring rates (K), and all three of out units are fitted with the Goldmund thread-on cones as specified.
So, not knowing exactly what you did, or didn't do, what materials you used, and how you measured/heard the results differently than we did, I really can't say why your attempt was so unsuccessful? I'd be happy to assist you if you like, however.