I’m not Greg. Sorry.
Clavicular breathing, aka upper lobar breathing, is negative when that is your primary breathing style. The brass teachers are trying to teach kids to take full breaths. Shallow breathing while playing an instrument can lead to musical and physical problems. Clavicular breathing is better than shallow breathing using mainly the muscles between the ribs. Breathing in this manner puts a person at risk of hyperventilating. This is not what you are practicing. You are learning to fill from the bottom up.
I would say if you feel more relaxed and open while releasing air into the horn, go for it; however, you are going to have negative tension if you leave your shoulders raised while playing. I am sure you are not doing that. But I wonder if the effort of raising your shoulders is worth effort. A full breath is going to cause the whole chest to expand and displace some organs in the abdomen. This means that upper parts of the chest are going to increase in girth and naturally push the shoulders up. I wonder if raising your shoulder is effiecent add-on to taking a deep breath? Can you take a quick, deep breath between phrases using wedge breathing?
I look forward to the teacher’s view.