I'll have to measure when I get home to sit in my LP seat, but IIRC, 42" is what I use for ear height.
The 876 is 37.4 and looking at it, you would subtract ~3" to get center of the tweeter at 34.4. Still, something is wrong, because with the 8" of lift (which would put them at 42.4", they are still slightly below my ear level.
As for the other Vento towers, here is a photo with the 896, 886, and 876 (and the rest of the Vento family) in a row. As you can see, if simply standing without any special setup, the 876 has the highest tweeter!
Using a rough estimate, the 896.2 (I assume they did not change height from 896) is 43.3 tall subtract off 7" for the mid-range and an inch above and below and you are down to 34.3", then another 1.5 inches to get to the center of the tweeter and you are at 32.7"! Of course tilting it back a few degrees and elevating it can make up the difference!