The standoff height is the distance between the tip of the mixing tube and the material. A standoff too high causes dimensional problems and alters the top edge created by the jet as it gradually widens in open air. Standoff too low risks scratching material on rapid traverse between cut paths, or snapping the tube causing downtime, cost, and angry operators. Standoff height should be approximately the thickness of a coin (varies depending on your nationality, obviously) – about 0.100” (2.54 mm).
I guess I could end the blog right here, but I think there are a few more things you might want to know about standoff height.