As an American who has gotten very used to metric units in studying engineering, the general rule I picked up is that you typically only change units every three orders of magnitude. So 8 decameters would typically be expressed as 80 meters, maybe 0.08 kilometers. Decameters and hectometers are a thing, but they’re not common units. Even centimeters don’t see much use compared to millimeters.
If I were writing the Star Wars movies with the benefit of hindsight, I would allude to the fact that Vader seems much more aggressive when dealing with Leia compared to other Rebels, like something about her Force aura is triggering to him.