How do you determine absorbtion panel placement

I have Maggies mmg, Apogee Centaurs, and Gallo 3.1 speakers. I made two 72"x24" and four 48"x24" absortion panels with acoustic ceiling panels. I removed the covering side that faces the room from the ceiling panels. My main concerns are how to determine the absrobtion panel placement for the Maggies. My room is 27'x24'x7'. The Maggies are 83" from the back wall, 71" from the side walls and 8' apart.