To the best of my understanding, both your composition and your Zax object need to be centred first. Therefore, your plane needs to be exactly midpoint vertically in the composition, and your object sitting in the crosshairs within Zax. From there you can plot a point that is off-centre with reasonable results. It worked just fine for me this weekend. I plotted 25 sets of table and chairs onto a conference room floor, then took 4 different POVs.