Oh now I got It. Well there is two ways you can dodge projectiles.
1. By using reactor (Z key) to escape close ones.
2. Wait before boss atacks and when it does move in any direction where projectiles will not reach you. After that you'll have some time to sneak behind his back and hit it.
Yes sometimes boss stays on place for a longer time than it should be. It has to do with the way he's programmed. He has two basic states of behavior: move & stand. And these states are randomly applied via timer. So it can easily recieve stand > stand > stand command.
Wish you luck :)