One thing I can suggest if you're having issues with fit: If you don't already have it, pick up a Zeagle Split Saddle Strap Assembly - BCD Accessories - Scuba Equipment Dive Gear Best Prices to keep the BC from riding up on your shoulders. It does an excellent job of holding it down without being uncomfortable.
After rereading your post a couple of times....do you only have one trim pocket on the upper cam band? If so, you should really have two; one on each side of the tank. That would allow you 10 lbs on your back with just those two, not to mention it will help keep you from rolling side to side during the dive. Add a second pair and you can theoretically have 20 lbs on your back if necessary.
And aside from the difference in lift capacity (45 lbs vs 35 lbs), that's the main difference between the Ranger and the Brigade. The Brigade uses an Escape bladder with bungee wrapped around it to create those pockets. Like you, when working with students, I too tend to dive with a little extra weight, just in case one of them decides to bolt for the surface or get into an uncontrolled ascent situation. Try moving your trim pockets to the top cam band and put the bulk of your weight in them and see if that doesn't help keep you in more of a horizontal position. It definitely made a difference for me.
Picked up the Saddle Strap and it did make a difference. I do have 2 trim pockets on the top band.
This last weekend I stole my Son's Rangers and what a difference. My son has a Medium, where I have a large. I bought the Ranger from my first LDS a couple months after getting certified and never really looked up the sizing chart as Owner said the large would be perfect. I am 5'7" 160-165 lbs., 30/31" waist and 17" shoulders. So looking at he Zeagle Charts, I should have been in a Small.
How much of a difference should could make, or do I just have some mental block, or suck. lol
Vest Measure Waist Size Shoulder Measure Shoulder to Waist
SM 28"-35" SM 14"-18"
MD 33"-41" MD 18"-22"
LG 37"-45" LG 22"-26"
XL 42"-50" XL 26"-29"
XXL Custom XXL Custom