Lighting a large backdrop from one side with Selador Vivid

I designed in a theater with Seladors on top and bottom.  It was extremely difficult to get a good wash, but with some experimenting I was able to greatly improve the house wash.  It is extremely important to have the correct lenses, which this theater did not.  You'll need two lenses, both horizontal and vertical, of the appropriate spread, which depends on the size of the drop.  ETC has an excellent application note with good analysis and lens recommendations.  Another app note has detailed recommendations for a single row.  I don't see any reason you could not get a nice wash from top only with the double yokes and appropriate lenses.  

These lenses do not have the typical gradation of a SkyCyc or similar instrument.  Instead they concentrate the light in the center and it drops off from there.  if you aim for the middle of the top half and the middle of the bottom half, you'll get a good wash that should merge in the middle, but drop off a little at the top and bottom.