Well, one thing to consider (and this is just a theory here) but if they are filming the Smallville scenes first and Clark is depicted as he is in high school or college, Cavill might have been required to only bulk up so much. It's possible that he might get bigger in the coming weeks/months whenever they start filming the Metropolis scenes.
Again, just a theory. I don't know what their shooting schedule is. His build (IMO) looks fine but I just thought I'd bring this up in case anyone is worried he isn't big enough.