The earnings can be greater with Shift penalties and overtime as explained in the letter.
But the following implies it is normal to get shift penalties :
"A level 13 multiple licensed Qantas LAME working the Domestic 12 hour roster earns $134,300 including shift penalties."
and doesn't mention overtime, so would this be on top of the $150k?
Seems to me a similar tactic to Qantas use in statements about 30%+ pay rises, just be selective in what you include and exclude.
And just how many of Qantas LAMEs are level 13?