I disagree; if you add more units per room, you can use fewer floors to put in the same unit count, which allows you to add more traps on the now-empty rooms, which may make the difference. It also increases the number of enemies in the room since more units are blocking them, which makes AoEs better.
Still, it's a bug, so not something to abuse if you want to beat it "fairly."
Still, it's a bug, so not something to abuse if you want to beat it "fairly."