well strictly put, they still enter and start a close combat fight right on OR they can shoot at you first (from outside the board) before entering it. Since the rule state, that when the token is occupied by another drone, then they start their movement outside and then spend a movement point to move unto the board. Same logic would be applied if an "enemy" model is occupying the tile.
I am sure I saw this covered in a FAQ
not answered yet but Loig has picked up on it.