But then, his illustrations for CoH are very much on the impressionist side -- he doesn't even depict Glaurung fully at any point. He's both following the text there, and enjoying the liberty to create atmosphere instead of the hard detail, as he did on the films.
Use of a term like "liberty" in duscussing what an illustrator does with Tolkien illustrations is an oxymoron. Ted Nasmith has said that the Estate was very much involved in what he could and could not depict in his SILMARALLION illustrations. One of the things they did not want depicted was what CT refers to as "monsters". The Estate prefers landscapes and less defined illustrations.
Perhaps this explains the change in cover from Glaurung to a single figure on an epic landscape. I greatly preferred the dragon.