Positionals suck. Even assuming you remembered them flawlessly it doesn't matter. The tank just moves the boss and suddenly you have a choice of either missing the positional or wasting the GCD. Both are a DPS loss at no fault of your own. Or the boss just switches into a new mechanic that makes it zoom across the map, darting everywhere. Or the boss just has such a gigantic hitbox and they're on the edge of the map floating and you can only hit them from the front.

Just remove them from the game. Or make it so that attacking things from the back just gives you a flat bonus in DPS. Because then at least there wouldn't be this weird mental hangup that makes you go "do I need to be at the flank or the back" which can cost you a GCD while your attention is spent trying to stay alive or not wipe the raid. DPS rotations should be automatic, muscle reflex that you never have to think about so you can actually focus on the fun part of the fight. The fight itself.