If you look at ABC's Vote compass, Labor and Liberal aren't far from the middle, and relatively speaking aren't far from each other.All they have to do is be closer to right on labors left than the liberals are closer to the left on labors right. Do that and they can impact nearly every policy labor puts to the senate.
The Greens on the other hand
...So far left if you zoom in 20% they'll disappear off to the side.