I would not have a problem with a student questioning what or why something was being done; in fact, I would welcome it. That is a teachable moment. Dismissing a student for asking a question because the teacher feels challenged, stops the educational process. The basis for learning is to question. Once that stops, so does growth. Don't stop asking questions and don't stop looking for any an all materials that can assist you with better performance. When volume is discussed it also has a lot to do with breathing and hooking the head structure up to the air stream to all the muscles to function. Making a blanket statement on "How loud to practice" cannot be answered directly without taking into account what is going on in other areas of your playing. Are you connected to your crown tooth and have lower jaw function? How and to what level is your airsteam currently developed? What aspect of growth are you trying to achieve? What musical notational challenges are being presented to you in your playing? Volume is only one measure of an over all performance. Tone, Intonation, Range, and Tempo also figure into the releationship of your embouchure and it's muscular functioning. All of these factors must be accounted for in relation to Volume. Talk with your teacher and if you are not getting answers that make sense to you, inquire with someone else.