The space is not behind your ears....
Correct proprioception can be essential to great singing. When we don't have an accurate idea of what is *actually* happening, or where the sound is actually able to travel, then we can end up forcing our vocal tract into incorrect positions, creating tension in the extrinsic and intrinsic laryngeal musculature.
Let's start with a visual of what our vocal tract looks like
Take a look at these diagrams below...
Hopefully, what you can see from these diagrams is that our pharyngeal area occurs in a narrow portion IN FRONT of our ears.... NOT in the back of our heads! In fact, the tissue comprising the back of the pharyngeal wall is very thin and is not capable of malleability. We have the ability to constrict our pharynx, but not the ability to widen it. "Widening" the pharynx only refers to the relaxation of the muscles out of a constrictive pattern. If you do not have this constrictive problem, you probably won't achieve a sensation of widening. See the problem here?
Maybe you have heard numerous times: "Feel like the sound is coming out of the back of your head", "Create the yawn space", "Feel your throat is expanding".
Now, all of these cues *can* potentially help someone who may be squeezing and constricting, or inadvertently pushing the voice forward aggressively. However, for the rest of us, these cues can be a recipe for disaster as we attempt to manipulate the pharyngeal walls and structures of the pharynx (i.e. the tongue) in an effort to "feel" more back space.
What are some symptoms of this? Lack of squillo in the sound, less carrying power, more vocal effort, difficult top notes & passaggio, difficulty transitioning registers... etc.
Some of you reading this may be thinking, "But I definitely feel back space when I am placing my voice correctly." In this case, I would say, "If it ain't broke, don't fix it." However, keep in mind that a sensation of a lot of back space can also be the tongue retracting into the back of the throat. If you have problems like I identified above, you may want to look into re-mapping this sensation of back space in your singing.
As you're experimenting this week, see what can be accomplished without feeling too much manipulation of the space in the throat. Can you achieve a high, ringing head tone placement with lack of sensation in the throat? If so, you are on the right path! Keep in mind that these "correct" sounds may not be the most aesthetically pleasing close up, or in a small room, but these are the sounds that carry in a theater and create beauty, depth, and color in a voice over an orchestra.