"She had a very good base put into her at Tony's (Ottobre, owner) and then we did the latter part at Cranbourne and what we saw early was that she was more forward than what you would expect," Turnbull said.
"We stepped her up incrementally due to that and that's what gave us the confidence to go one jumpout, which was a strong hitout, into the 1800.
"We thought, low field-size (and) less pressure, she wouldn't get taken on with what was in the field and it worked out a treat.
"At this stage it's all systems go."
The TAB Australian Cup will be only the second Southern Hemisphere start for Middle Earth, a well-performed European who was bought midway through last year to be a Cups contender, but didn't get too the races until the March 8 Australian Cup Prelude (2000m), which he won.
"He's got decent form in Europe and he's one of those higher-class gallopers that could do anything," Turnbull said.
"He will stay further than 2000, we know that, but while he's sharp and early in his prep we thought we'd give him a crack at the Australian Cup."
All-Star Mile third placegetter Light Infantry Man is another import who is finally delivering on the promise he showed the other side of the equator and Turnbull is excited about seeing him at 2000m.
"If you had have asked Ciaron and I 12 months ago if he would run third in an All-Star Mile we probably would have said no," Turnbull said.
"But since Perth and that last prep, after he won the Northerly (Stakes), he's just kept improving physically and in the mind and that's obviously showing raceday."
2025 TAB Australian Cup full field HERE