I'm a dinosaur.
Yep, me too. However, we go one step further and measure in feet and meters and compare the two. A good blunder check.
I use a pocket rod to measure up to the knob on the tripod that is used to tighten the tribrach down and add 1.20' to this reading to get the total HI on my leica instruments, as stated the instrument center and target heights are the same, so it works weather you are setting up the instrument or target. I try to keep the leveling screws near the mid-range line and level the tripod head with the legs so that the height will nearly be a constant, but after all when you are using three tripods for traversing the only thing the HI is doing is setting the ground elevation of the traverse nail for future use and should be within 0.01'.
Sound like the way to do it.
Ralph