there is not SET STANDARD, it depends on personnel and situation. In general:
First leg requures proper use of blocks and the ability to not be bothered by the 3 turn stagger. It is foolish in an evenly matched race to try to make up a 3 turn stagger like one might in an open 400. And if you are in an outside lane, when you hit the home stretch you could still have 130+ meters to run, not 100. So they must know all those things. With a 3 turn stagger the lead off person must be seasoned enough to know how to run 400m well given the uniqueness of the set up.
Leg 2 runs first turn in lanes, so a good place to put an 800m runner who does that and knows how to break gradually while avoiding trouble.
Sometimes when we are trying to run very fast against very strong competition we will front load the relay so we can "stay in it", and then just hope the last leg or 2 runs scared enough to pull something off or at least get a taste of what running really fast reuqires. Like at Penn RElays where positioning in a crowded field and getting noticed are the goal, we run fastest in first 2 legs.
When we are clearly the best, or have qualifying, we run slowest to fastest allowing our last 2 people to ensure the win or advancement with as little effort as possible.
Right now, because I have 2 800m runnners on the team, I go 2(400 runner),3, 4, 1(400m runner). I could never lead off either of our 2 800m runners.
There is no simple formula, your head coach could be right if he has the right reasoning, as could you. Nothing wrong with experimenting throughout the season so you have it right for when it counts come championship time