If you don't modify the pitch, how much error is there in the height value when you run the following?
Code:
import viz
import vizact
viz.go()
SENSOR_HEIGHT = 0.71
HEAD = 0
myHead = vrpn.addTracker( 'Tracker0@localhost', HEAD)
def printHeight():
print myHead.getPosition()[1] + SENSOR_HEIGHT
vizact.ontimer(1,printHeight)