Oh boy, 2 AM! Sorry I missed this post before.
If I'd hazard a guess at what my thought process was, the Fireproof Frock uses the extra robe as a second layer to keep out heat and absorb the Antifire. Though I'm not sure why it doesn't also offer a little protection against Ice in that case, maybe it's something to do with the magical Water component in the Land Coral.
I'll look through these items again, but usually these inconsistencies will likely have been to fit all the text in the window. I'll see if I can't smooth them out, though.