Cpt Claret,
Have no experience of flying in Oz, but your explaination of how things work does seem a bit strange.
In the UK, the TL is always physically above the TA by a maximum of 500' and minimum of 0'. Thus, a QNH of say 1010 with a 3000' TA will give a TL of FL35. Likewise, QNH 1016 in the same situation would give a TL of FL30. Thus, TL's are not generally published in the UK, navigation charts quoting "By ATC". In everyday operations, we would not even be told the TL as ATC take care of things.
As a result, seperation of a/c on STD and QNH is made simple - standard 1000' seperation by ATC guarentee's that the physical seperation will be at least 1000', possibly up to 1500'. I can't comment on other states, so forgive my ignornce!
Regards,
Cuban_8