B15M,
After reading Manny’s response, it sounds like he is addressing the question from the perspective of finding the best sound for any given tuning slide position (deep into the sound).
I’ve thought about your question, and while I have a good answer that applies in many cases, I think you might benefit from reading several posts that made me reconsider my unwavering position on the resonant center of the instrument for a given note.
Have a look at a post by Peter Bond in a topic called
Resonance and Sound where he responds to my post and talks about tuning using a credit card. Then scroll down 5 posts and read his next post where he provides some very insightful comments about different types of sound production. He compares the “very razor’s edge of the sound” versus “playing deep into the center”.
I am in the camp of playing deep into the center of the sound. This sounds like what your teacher was trying to communicate to you. There is a lot of merit in understanding this concept, but there are other valid approaches to sound production.
Does this help?