Hello. If the tank is not positioning well a boss or mob, you can tell him, he might not have noticed the problem or be new at the place.

In CT some people remind the tank in jokes not to put the Valefor's tail looking to the group, just in case the tank is new. If the tank says he is new the other tank can explain a bit too. Many CT problems are caused by lack of communication.

In low level dungeons it may well be the tank is new or he is too busy trying to survive and is concentrating in other more urgent things (from his point of view) and forgets to place the boss where he can be well attacked by melee DPS or will not throw an attack to the group.

A quick ask can make him do it right (if he manages to read the chat log before a wipe...lol)

The more exp somebody has in a place, the more aware to every aspect of the fight he will be, the better he will place the boss, knows his attacks, he can anticipate where the adds are going to spawn and place the boss in advance, etc.

When things go south problems usually accumulate. Normally it's not just the tank has placed the boss badly, he probably is in low health and the rest of the party too, he might be worried about losing hate to an add, the healer is overloaded with work, casters are moving around avoiding attacks and can't cast well, etc.