Well, I agree that he doesn't look very muscled in any of the pics. The description says he is though, but maybe Fisher is basing herself somewhat off the book description as well.

He looks good in the photos in the movie guide and the Visual Companion though. Large but lean, rather than muscular.

They do mention CGI work on him as well so I think that in the film he will look more grand than in all the promo pics.

On the other hand, maybe not, maybe they've really gone for a kind of toned down design, one that's more low key.