I'm pretty sure the Gorean ideal of beauty has a lot to do with JN's personal ideal of beauty.
It's plain he has a fondness for shorter women with curvier figures but there are also slaves in the books who are described as both slender and very beautiful so his tastes are not confined to any one particular type.
I don't agree that "plus-size" models, or at least the fatter ones, represent a JN/Gorean ideal of beauty, except perhaps for some men of the Tahari who seem to have a thing for overweight women. Whenever we are given details of heights, weights, measurements in the books of slaves considered to be very attractive they turn out to be pretty petite and well within normal weight ranges - for example, Doreen in Dancer is repeatedly described as curvy, with ample boobage, curvy hips and a belly and her BMI (which I know is an imperfect measurement) comes out as 21.
The other thing that seems to be a JN fixation is the high regard given to auburn hair. It comes up again and again in the books as the ideal hair colour. I suspect JN must have had his heart broken by a girl with auburn hair.
It is regarded as right to enslave a natural slave