All of my ferrets are Marshalls (Petco), but some of the differences are male to female as well not necessarily breeder.
I have a stocky boy that looks a lot like Meechy, and I have a smaller slimmer boy as well. My girl also has a slim face and kind of mousey features, and is quite dainty :)
I did notice some breeders have large males due to when they are fixed.
Heres Rambo, I think he and Meechy could be brothers :)
Rambo is MUCH larger than bear, although supposedly at least 6 months younger than Bear
Heres Bear (stealing my stuff >.>):
He seems to be a little smaller for a male and feels petite. I don't know why this would be, maybe just a smaller litter?
Toki is my girl, she has similar features to what you describe Mina to be. I think I read that these are gender differencess:
She's definitely pear shaped as well, most of her weight is in her bottom end/belly. It has been difficult to keep her in her harness when we go outside since she just rolls it off of herself lol.