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.
Both Maggies and Apogees have very narrow dispersion patterns(little worry of side reflections), and will benefit most from their rear radiation being diffused(rather than absorbed), for more sound stage depth. In their case; diffuser panels(like the RPG Skyline), directly in line with their rear radiation, is best.
Ribbon and electrostatic speakers do have different dispersion patterns from dynamic speakers.
Typically, sitting in the sweet spot, move a door mirror (Home Depot or Bed, Bath for a few dollars) along the sidewalls or ceiling. When you see the speaker in the mirror, that is where you place the absorption panel.
That would be for speakers with wide dispersion. Not an issue with narrow dispersion, especially with the distance you have from your side walls.