PLS chart, page-3731

Those centre point portions are from dark pool orders (centre point) they are not visible, not half way matching between regular orders. The orders you see on the screen are what's called lit market. The orders between them are called dark pool orders.
If you put buy at market order and I put sell at market order at the same time: latency arbitrage algos will jump in, buy all or part of my order and put it in centrepoint for you for little bit extra than they bought of me. Together with quickly trading order spread difference between ChiX, ASX, etc to skim few cents. And add to dark pool orders from high frequency algos already there.
The rest of your order will get matched up the regular ASX way:
If I put 2,000 shares buy order and you put 5,000 shares sell order, current buy/sell spread is 2.285 / 2.29: our orders will get executed @ 2.285 and rest of your order from remaining at price orders 2.285 queue
Dark pool orders basically jump the queue and ensure execution for those that put them in. But 2 regular orders won't get matched at centrepoint without 3rd party skimming the trade between the 2.

Hope that makes sense