Hi,
Typically I like height to be between the center of the tweeter and that of the midrange in a quasi-pointsource like VR-5s. Having said that, the wide and even off axis response of the VRs both vertically and horizontally make relative height not much of a concern. I think whatever looks most comfortable to you from the listening position should do the trick. Balance hardly changes over a few inches of difference in seated height. Enjoy!