Ah.This shows the bar (my nests will look different), see where it shows 12" front to back for the nests? Then doesn't gove a measurement from the front of the nest to the perch/bar/landing place. I'm not sure what to call it.
I don't think Australops would need help to get in there, so you could probably just skip that front perch.
But if you want to have one, I would follow @aart 's advice