The only thing I can think of as a negative is that the t-valve might open too late with the increased spring pressure. It's gonna be a trial and error adjustment but I think you're on the right track. There's a slight increase in pressure with the thermo unit vs. wide open and the Bassett spring is fairly light and sensitive.
If you have further problems after tightening up the spring you might PM LVjetboy. I think that's his diagram and he's done more research and screwing with this stuff than probably everyone else on the forum combined. (no offence jer).
If you need assistance feel free to call us Taylorman.