Ciaron Maher is keeping his options open with classy mare Set Square who could join stablemate Jameka in the Group One Turnbull Stakes.

Maher said Set Square would be a dual acceptor for Sunday's Turnbull (2000m) and Friday night's JRA Cup (2040m) at Moonee Valley.

Both Jameka and Set Square are on a Caulfield Cup path, with Jameka's dominant last-start win in the Naturalism Stakes giving her an automatic berth in the race.

Set Square had a wider run than her stablemate and ran fourth in the Naturalism.

Maher said he had increased Set Square's workload heading into her next assignment because he felt she overdid it lsat start.

He does not believe there is much between the mares who have won the past two VRC Oaks.

"Jameka probably makes her own luck a bit, but they're both high quality horses," the trainer said.

Maher said he was rapt to see Jameka so dominant in the Naturalism and was happy with how both mares' spring preparations were tracking.

"They're in good order. Now they are getting out to their trips and their preparations are going well. So far so good, touch wood," he said.

Set Square has 57kg for the JRA Cup and is among 26 nominations while the Turnbull Stakes has attracted 20 entries headlined by in-form Godolphin-owned gelding Hartnell, the winner of the Chelmsford Stakes and Hill Stakes in Sydney by big margins at his past two starts.

Jameka has 54.5kg in the Turnbull with Set Square on 55.5kg.

Set Square was a luckless third in last year''s Turnbull Stakes and Maher said she was in similar form.

Hartnell is the $2.25 Turnbull Stakes favourite ahead of acceptances with Ranvet Stakes winner The United States at $5.50 and Jameka at $6.50.

Jameka has two wins and a placing from three runs at 2000m while she also performs well at Flemington having won there twice including last year's Oaks.