Miller is chasing his third success in the Northam Stakes after previous wins with Power Princess (2011) and First Among Equals (2017).
Since the Northam Stakes was first run in 2007, Jim Taylor holds the training record after preparing Vain Raider (2009), Barakey (2013) and Magnifisio (2014).
Flirtini was unplaced in all four starts at last year's Ascot carnival, but Miller believes there were positive signs on her return in the Marjorie Charleson (1200m).
The Artie Schiller mare settled last in the small field of six and was doing her best work late in the straight when 1 ½ lengths third behind stable mate Amasenus.
Miller took confidence out of the run and said it showed the six-year-old, fifth in last year's Northam Stakes, still maintained an appetite for racing.
A dual G3 winner with over $609,650 in prizemoney, Flirtini carries 54.5kg for in-form hoop, Lucy Warwick and has drawn barrier six.
Miller says there are several pivotal factors in Flirtini's favour.
"The other day she was good, "Miller said on Tabradio.
"They didn't go quick for her and when they let rip, they let rip quick and she was sort of off the bit and got going late.
"She will get genuine tempo in this race and has drawn a gate.
"With that weight, gees, she has got to be in with a chance.
"Light weight and back to 1100m you can make a case for her.
"But I'm a realist as well and know she is nearing the end.
"She will run extremely well if she's at the top of her game."
Meanwhile Miller says Amasenus faces a distance query in a bid to win consecutive major races at Ascot on Saturday.
After taking out the Marjorie Charleson (1200m), the five-year-old is searching for her first 1400m win the Sheila Gwynne Classic.
"1400m is an interesting one, does she get it?" Miller said.
"She is racing a lot better than what she was when I gave her a crack at it years ago
"She has an unbelievable burst of speed and hold onto her and wait to pull the trigger.
"What better way to find out if she gets 1400m against your own sex at set weights and penalties."