I'm trying to get some better standings with the Amarr Empire and the Emperor Family corporation to reduce the broker fees when trading with my alt. This is already a rather annoying process, and receiving storyline missions from the wrong corporation makes it even slower. The storyline missions are responsible for a large part of the total standing gains, I don't want to waste them on a meaningless corporation.
How is the corporation for the storyline mission determined? How can I make sure to receive a storyline mission of the same corporation I'm running missions for? How would this work specifically if I want to gain standing for the Emperor Family corporation and can only fly distribution missions?