At a Master Class and acoustics lecture this month, I picked up on some new language regarding how we can talk about dropping the jaw, the sensation of pharyngeal space, and creating "warmth" in the sound.
This instructor emphasized that is important to map the back of the throat to where it truly ends, right by the ears. When singers imagine the back of their throats going beyond that, or the need to create extra space behind the tongue , this is almost always done by pulling the tongue back and over depressing the larynx. It is hard to for most people to interpret the idea of "creating space" as a passive sensation. They want to do something, which usually results in the tongue pulling back, which ironically creates even less space in the pharynx.
This is why many people think the /a/ vowel has the most space behind the tongue and /i/ has the least space behind the tongue. In reality it is the opposite. We take the information from the front of the mouth, I see a larger mouth opening for /a/ so therefore there most be a larger opening everywhere. I see a smaller mouth opening for /i/, it therefore must be narrower everywhere. When creating an /i/, I also have no sensation in the pharynx or behind the tongue. I therefore assume I'm not doing enough, not creating space.