Yeah I'm thinking now that Esmenet was raped by the bird-Synthese. And honestly, given certain real life avians, a giant (relative to the body that possesses it) extrudable penis isn't actually that weird or implausible. And is exactly the kind of thing an Inchoroi would make sure its vessel had.
So the human figure was a glamour. Yes, the glamour around Golgotterath had additional properties, but that was a glamour to end all glamours, and shouldn't be taken as typical, I think.
I find it interesting that as Esmenet leaves the Gate of Pelts, she imagines the World as a prison because leaving Sumna is nothing (p292). Why a prison, I wonder? Does it reflect her feeling trapped by her circumstances in life?
She identified Sumna with her imprisonment (though it's more a metaphorical prison describing the role she's forced to play in her life). But when she left Sumna, she felt nothing. No sense of escape or danger or accomplishment. She still feels a prisoner. So she moves the frame of her prison to encompass the entire world.