You should just script it so that when the box or w/e is thrown at the door, it gives the grunt a pathnode to the player.
Do this by checking for a box - door collision with the EntityCollideCallback.
You can also add some scripts to check whether the box was thrown fast enough if you want. This will mean no matter how far away the monster is, you can be certain he will 'detect' the throw.
Quote:This can be adjusted in the user defined variables.
I usually only modify user_defined_variables when there is no simple way to do it in script. For example, I just modified the block_box entity to be made of metal, because there was no other easy solution I could think of in script.