But i have also experiemced different heights in the T track i have purchased.
Started out using Rockler then somewhere i purchased a couple of intersecting cross joint pieces and they were higher than the norm.
Seems some can take the head of a hex bolt and others only the flat t shaped bolt.
As long as you stick to a particular manufacturer all is cool.
Kreg has some nice extrusions worth looking at also for the fence top to hold hold downs.