Density seems fine to me. It get’s higher with each difficulty, also do not forget that some monster packs have a trigger range, which means they do not appear if you don’t walk into them, like the wraiths and spikeshells.
In Normal it was pretty empty, but that’s kinda to be expected on normal. Running through the area on Ultimate the areas were a lot more populated, so I’m guessing it’s either RNG or dependent on difficulty.