I guessed the same, on that floor the further away you are from the coloseum, the stronger the monsters.
Why ? They escaped the coloseum trials and further infighting.
The first skullsheep used camouflage and wait for an opportunity to strike.
The closer we got to the coloseum, the monster acted with less wits.
So the menace shifted from single monsters with some level of intelligence, to large numbers but without any strategy/wits.
Danger is still there because our pair doesn't have any more bombs to clear a path.