I'm not sure of your question but it sounds like you are asking how much the light mover can lower your light? When I installed my light mover, I wanted it higher so I looked at the opposite... There are multiple connection points between the light mover and the light providing multiple options for raising/lowering.
@chiqifella's reference to clouds outdoors sums up my view also... Drawing 5 watts of power, I believe it has upped my yields. I find that it's more useful for spreading out the heat than dramatically increasing grow space sq. footage. I usually adjust the distance the light mover travels as the grow progresses... wide travel early in flower, narrowing the distance as the grow progresses... It's not adding extra light so, the more travel, the less light intensity at the plant so you really don't want that much travel. With a fixed 1000 watt HPS, the hot spot is hotter and smaller, requiring diligence to keep the plants from growing into the hot spot... Just keep in mind that, when power goes out, the hot lamp stops wherever it is... Even the heat emanating from this recently turned off lamp can fry flowers that are unlucky to be underneath... Best of luck!