I do see your point.
But there are 2 different things the price people pay or think wjat its worth and then there is what the bank thinks its worth.
I have heard horror stories about queensland and w.a
People paying for property expecting to get a loan only for the bank to turnaround and say nope not worth that. We think its worth this much.
Less than 20 you would be pushing it.
Income does play a part but is not everything.