we know chorae when touching skin (organic/bios such as men or sranc) impart protection to the whole organism from sorcery. there must be lines of conduction for the chorae effect that work to conduct the effect along organic tissue.
An example of chorae not touching skin but used to confer protection to an inorganic material are kells circumfrix which had three bound to the bronze ring
A great tree soared into the night sky, a hoary old eucalyptus, too ancient not to be named. His first thought was to set it alight, to transform it into a blazing beacon of his wrath—a funeral pyre for the betrayer, the seducer! But he could sense the absences that encircled the man, the three Chorae the Men of the Tusk had bound to his bronze ring. And he could see that he suffered . . .
and the no-gods carapace which is apparently an iron sarcophagus that legend states has 11 chorae bound to it, tho there is another quote that tells us the carapace is actually nimil and covered in choric script.
No-God—Also known as Mog-Pharau, Tsurumah, and Mursiris. The entity summoned by the Consult to bring about the Apocalypse. Very little is known about the No-God, save that he utterly lacks remorse or compassion and possesses terrible power, including the ability to control Sranc, Bashrag, and Wracu as extensions of his own will. Because of his armour (the so-called Carapace), which eyewitnesses describe as an iron sarcophagus suspended in the heart of a mountainous whirlwind, it is not even known whether he is a creature of flesh or of spirit. According to Mandate scholars, the Inchoroi worship him as their saviour, as do—according to some—the Scylvendi.
Somehow, his mere existence is antithetical to human life: during the entirety of the Apocalypse, not one infant drew breath—all were stillborn. He is apparently immune to sorcery (according to legend, eleven Chorae are embedded in the Carapace). The Heron Spear is the only known weapon that can harm him.
Secrets . . . Secrets! Not even the No-God could build walls against what was forgotten! Seswatha glimpsed the unholy Carapace shining in the whirlwind’s heart, a nimil sarcophagus sheathed in choric script, hanging . . .
going a bit off topic but assuming that the people werent just using a large number of chorae than necessary,then when chorae are used to protect relatively inorganic material there seems to be a need for an exponential number to impart protection from sorcery to these materials. How does this relate to wracu and why they dont just use chorae to protect themselves comes in how they describe their physiology
"FOOL. I AM THE FIRST. MY HIDE IS BRONZE. MY BONES ARE IRON!"
There must be a bios component to the wracu but if their physiology is primary inorganic particularly on their outside, perhaps it doesnt confer the protective effect of chorae very well and they would literally need to be covered head to claw in them and then some for it offer true protection
....or maybe its wracu-nature retcon [reasons] related