Here are the relevant references from the Books where Cleavage is mentioned.
I make no pronouncements on these matters, but report them as I find them.
Arrive at your own conclusions.
I wish you well,
I could see the lovely curves of the interior cleavage of her breasts, revealed in the parting of the rough slave tunic.
The grass was to the knees of the kaiila. It came to the thighs of the slave girls, in brief one-piece slave tunics, of brown rep-cloth, with deep cleavages, in throat coffle, bearing burdens on their heads.
"Consider the brevity of her tunic," he said, "its cleavage, its sleevelessness, the slashes at the hem of the skirt.