Having it not do anything in the case of partials actually "feels" more right to me... OTOH you could have it burn up all remaining levels for a chance equal to the ratio between the remaining levels on the Orbiting Ray and the level of the incoming ray.

Also, the name is the wrong idea... it isn't a ray it does things to Rays...
Better might be: Ray Orbiter, Capture Rays, or Smerg's Ray Catcher.