A question for the ages, I've had identicle teles, in every respect, same setup, bridges, nut adjustments, neck relief, radius, string heigth, string guage, brand of strings, frets types, shimming the neck angle on and on etc. etc.....
and still the string tension or slack as you call it is significantly different.
That's one of those kooky variables that I learned to let go, even with my overly obsessive nature, it's just one of those things in life that just are what they are.
Some guitars, teles or otherwise are just stiffers!
Great question though.
I'd love to hear a definetive answer that actually works in that situation, but I gave up pondering that imponderable a long time ago.