I found the reference in one of my books:
"Massassi hangar, interior: “Thet had one complete X-Wing, a Y-Wing and some bits and pieces, painted ships. SO I took the plate, reduced it, and then put it down in the left centre; then I took the same plate, reduced it even more, and put it in the background on the right hand side of the frame; then I painted around it, just lots of little lights in the back, a couple of shapes, a few hoses hanging down. Youd be amazed how little is on that painting”
For a long time I actually thought they took the painting with them on set.