Tilt is truly critical for the Vandersteens, for imaging and tonality, so spend the time to get it right.
I owned Quatro's for a happy while, and I found that the foolproof way to get this done in my room was to use a level with a laser pointer. I would set this level on top of the wooden cap and project the beam to where my listening position was. There I had paper on a stand that the beam illuminated, and I would mark the location of Ear Height + Offset (from Tweeter to Laser position on the Cap). When I got the beam to hit that point, everything snapped into focus amazingly well, with proper tonality, importantly. Get this right on one side and then tilt the other to match the same spot.
I owned Quatro's for a happy while, and I found that the foolproof way to get this done in my room was to use a level with a laser pointer. I would set this level on top of the wooden cap and project the beam to where my listening position was. There I had paper on a stand that the beam illuminated, and I would mark the location of Ear Height + Offset (from Tweeter to Laser position on the Cap). When I got the beam to hit that point, everything snapped into focus amazingly well, with proper tonality, importantly. Get this right on one side and then tilt the other to match the same spot.