You can't use shares you bought after sell event to offset the...

You can't use shares you bought after sell event to offset the profit at the time of sale for Tax purposes.
It doesn't work like that, even if it's in the same financial year.
Your portfolio averages will give you skewed picture of profit and loss for the financial year.

In a nutshell: You're using the shares you bought after you sold a parcels to erase original profit through average purchase price calculations.

That's what it looks like to me, from your examples and questions.
There is also difference in the way tax is calculated if you are deemed to be investor or trader.

Again, your accountant will be in much better position to determine what you must do in your circumstances, to avoid trigger of any of ATO tax avaidonce rules..
If your accountant says you must pay tax on $23k it must be a good reason for it.