Are you serious? They are on a collision course!
Have you carefully looked at the data in the report? I have, probably a dozen or more times now. Even with the worst interpretation of the TCAS, the GA-8 was passing behind the jet (then somehow caught up after the jet turned final/upwind).
An object far away will appear stationary in the windscreen even if you're not on a collision course. The "stationary in the windscreen" idea is that it remains stationary up to the point of impact. You don't run into everything that appears stationary in the windscreen.
At the beginning the jet was on base leg about 2.5 - 3 miles out, and the tracks suggest it was about 90 seconds from the threshold (does that sound the right ballpark?)
The GA-8 was on a 4.5 mile final which I would expect to take 3-4 minutes, giving around 2 minutes separation at the threshold.
If the jet continued straight from base leg and crossed final at 90 degrees things could have been close, but they don't, they have to turn final which puts them well ahead of the GA-8 and you would expect separation to increase from there.
This is a little concerning Andrewr. The big picture here is that a jet's airspace was compromised by a light aircraft
If 2 miles and 500 feet isn't sufficient then what is? CASA recommend 2000 AGL overflys - 500 feet above the high performance circuit height - so they presumably think it's OK. The only alternative is no RPT without CTA - and that equation is pretty much guaranteed to give less RPT not more CTA.
I don't see any evidence that the jets airspace was actually compromised. It's all about the TCAS which has some very suspect numbers for the horizontal position. If the TCAS data didn't show the suspect 200' 1/8 mile data, would there have been any investigation?