I have seen the etiquette for this vary between each dojo. Everyone follows the other students.
The best explanation I have heard is that placement of the blade reflects the level of trust you have for the people around you. Placing the sword in position easiest to draw (left side blade out) means you trust them the least. Placing the sword in hardest (while still within reach) position to draw (right side blade in) means you trust them the most. With all other positions falling in between.
I would advise following your sensei's habits (at the very least don't put it a more aggressive position).