That's kind of proving the opposite of what the OP is seeing (aka hearing).
As you go UP in Density Altitude (and Altitude in general) you actually have fewer air molecules. This is why the aircraft has to work harder for the same amount of lift to be generated than it does down lower.
Keep in mind that Density Altitude isn't an actual height but a numerical representation of how the air "acts/feels" when environmental factors are calculated into the equation. For instance, a local runway has an actual altitude of 4,000' MSL. But it's a very HOT and HUMID day so the the Density Altitude could be more like 7,500'MSL. This tells you that your aircraft will operate as if you were flying at 7,5000' instead of the actual 4,000' you're at which allows you to make more informed Aeronautical Decisions.
So as your UAS is flying in hair with a higher DA is is absolutely having to make adjustments to motor speed etc to compensate as compared to flying in a lower DA.