I've been to quite a few contests in which the physique class was contested and honestly, these guys are actually pretty darn muscular and fairly big. Of course I'm talking about decent level competitors not those doing novice shows.
In fact I've went to several bodybuilding shows and the good men physique guys were just as big an muscular as the bodybuilders in the middle classes (176lbs, 187lbs and even some 198lbs).
I find it funny that many people look at top physique competitors and say they want to be like that because they are "not too big"... well, let me honest 95% of those making these comments would not be able to achieve the size of the good men physique competitors even if they trained only for maximum muscle mass.
Honestly, you want to know how to build a body like the top physique competitors? Choose the right parents!
What I noticed is that physique competitors have the perfect natural aesthetic built: They have wide clavicles (which gives them broad shoulders), a shorter torso and longer limbs which gives them a more aesthetic look than those who have a longer torso an shorter limbs (who look blocky), a small waist (which creates the illusion of even wider shoulders) and small joints.
If you are not built like that, you will never look like a top physique competitor. Take me for example, I have a wide waist, a long torso, short arms and narrow clavicles. Even if I did everything in my power to emphasize the right muscles I would never have a ,male physique competitor look.
I think that you should train to build as muscle muscle overall as you can. Once you are at a very high level of development and you find yourself to have a body structure that might do well in physique then you might think about emphasizing certain muscle groups to create an illusion.
But unless you have A LOT of muscle already, focusing on building certain muscles solely to get a certain look is a mistake IMHO. You might get different answers from other coaches, but my belief is that you should strive to build your body as much as you can... your shape and structure will be revelled to you as you get more an more developed and that "look" is vastly genetic.
I'll give you an example. A good friend of mine is an IFBB pro bodybuilder. His partner is a physique competitor. They train the same way (of course, they are training partners) and the physique guy is about as strong (even stronger on some movements) yet they have completely different looks.
A pitbull can never become a greyhound even if he tries