::::::Maybe we could just say "An image of Achilles and Patroclus, presenting the mythological figures in the pederastic context common to Greece of the 5th century BCE"?  That's a bit more concise, and avoids the entire issue of whether the exposure of the genitals is specifically a sexual cue.  Besides, the issue of the varying presentations of the Achilles/Patroclus relationship isn't all that relevant here, really. —  •