There's an indefinable science at work in Caitlin Power's studio. We're halfway through model fitting day, five days before her 2014 spring/summer collection hits the runway, and designer Power is shuffling through racks of garments with Amanda Lao, her line's general manager and stylist.

Glancing at the wall of looks, the collection already transitions seamlessly from workwear (Power's signature) to weekend wear to evening, from one colour palette into another. But with 25 looks to match to 13 models, there are a thousand other concerns to be sorted, from "I don't think it's right for her complexion" to "She needs to be in either this dress or this dress" to "She's bigger in the bust, so she'll fill that piece out."

"It's so planned out it's crazy," Lao says.

Adds Power: "We always try to plan it out before, but it's so hard to know what the girls are gonna fit."

So how do you match the outfit to the person wearing it? "It's the overall look - some girls have the exact same body shape, but (a different) complexion, or attitude, they just fill it out more than some garments."

"I think when someone has it on, it either fits or it doesn't," Lao says. "Either they rock it and they own it, or it's not their outfit."

So you're waiting for that angels singing kind of moment? "Exactly," they chorus.

Occasionally, Power says, for tougher-to-fit items, they'll even send it to the modeling agency to find someone who can pull it off, instead of the other way around. She adds there are a few models they've hosted year in and year out, so they intuitively know what those women will look good wearing.

"When we cast, we definitely look for presence and a really strong walk," Power says. "The collection is that power woman - we don't usually cast new girls or young-looking girls."

"Unless they got it!" Lao interjects.

The collection is a punched-up take on Power's usual powerful, polished womenswear, inspired by a recent trip to St. Martin in the Caribbean. Lao was along for the ride, as well as Power's mom; the designer says she's excited for her mother to see how those memories translated on to the runway.

I ask Power what else she's looking forward to this week. "The day of," she says. "When the girls put their first looks on and they're in full hair and makeup and fully styled, and you're like, It's coming together. Then the music comes on and you're like, Ahhh!

"It's a really cool feeling, especially when you're backstage and you see it on the screen, just coming to life. And then it's done! And then it's over in like eight minutes! It's almost like a wedding. You plan for it, and plan for it..."

"Except," Lao jokes, "it's like, six months later you have another one!"

One of Power's usual models, a willowy brunette named Lauren, arrives for her fitting; after some chit-chat, she's put in a slim-cut skirt earmarked for the show's finale. `

"Looks good, I'm just worried about the walking," Power says.

They try pulling it up and down so it sits more on her waist or hips, then hand her a pair of the four-inch nude heels the models will be wearing at the show for a test runway walk - for the five or six paces the cramped studio allows.

"It mean, it fits her really well," Power says. "It looks, like, bomb." One more trial walk, and Power emits a high-pitched squeak of joy.

With that look locked down, Lauren clambers into pair of shorts - all, it must be said, while still wearing the stilettos.

I ask her if she's in any more shows this week. "Oh, no," she laughs. "I'm not really modeling anymore."

Lao interjects: "She's one of those ones we don't let go."

"They won't let me!"

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