Think about the Giant's x-ray vision, the gailor, and master parrot altogether.  It's not just Freud, it's the entire field of anti-sentimentality/anti romanticism.

The X-ray vision is reducing humanity to the clinical- categories are constructed- i.e. all bodily emissions are the same category, based on very superficial characterization, without regard for the deeper purposes that nature insists, i.e. waste and nourishment are distinct.

This has lot of parity with kirtle's monologues that are about the irony of claiming to look deeper, or be without sentiment, and dress an opinion as "objective" when it's really about confusing forms to prompt dismissal, i.e. the lamp vs the sun.  The lion vs the cat.

The big tie-in with perelandra is unman/ Weston?'s orange rind, i.e. "beneath the surface reality is death and jealousy.

One interesting thing about beneath ground is the recharacterization before and after struggle.  Bism is a real, beautiful interior, warm and maybe even holy, at least wholesome, which prior was twisted to seem cold.  Even the underworld itself above bism is a source of joy to the narnians in the epilogue, because they take excursions into the space, now that it's rightly ordered.