An odd one, this, in that I have a filled grid, with my replacements all working properly, and I think I get what's happening in word B (though I have it as two words). Word A I cannot see as a single word or how the four six letter words in the grid are examples except extremely tangentially.
So either my missing wordplay letters are wrong, or I'm just not seeing something obvious.
One of my missing letters could be one of three letters, Chambers giving alternate spellings for the word. All three letters create words that sort of work, but not so it makes much sense or one recognisable A word.
I'm not that worried: the grid fill works anyway and the letter in the blank space is fine. But it would be nice to know.