Changing origin of material for particle system (Help.)

Hi. for context this is what we are looking at. Right now it is a simple size by life. It expands in all direction from the center of the material to the initial size. I don’t want it to start from the center. I want to choose the location in which it starts to expand. In this case from the width of the rectangle facing the camera slowly getting larger to fill in the outline. Or if you know a better way to do this and I am being dumb about it please let me know. thank you all in advance.