Thanks for the comments, Fearn.
I was watching the other day the kyudo episode of the 'Samurai Spirit' [documentary] on NHK. And yes, having just learned what kyudo is, they do bare one part of the chest to facilitate the arrow shooting.
Which indeed makes one wonder whether perhaps the [Amazons] story is true.
In the
180 BC relief below, one of the Amazons is definitely showing one bare breast. And it seems to have been mastectomized (or was the relief just abraded over time?).