Acoustic panels on ceiling

The scientific way to do this is locate the sound pressure peaks greater than 6 dB above the average sound pressure in the room using a SPL meter and appropriate test tone. Otherwise, it’s like shooting blanks in the dark. It’s like trying to solve x simultaneous equations in x+n unknowns. 

…..you say you’ve been reading conflicting info. How are the answers on this thread any different from the rest?  Why wouldn't you be satisfied with whatever GIK tells you?  Just curious.

I would be very satisfied with GIK info if I were able to figure out those first reflection points myself. Totally my fault

I haven’t validated the calculations for accuracy, but quick scan of the numbers look good for this calculator. One of my friends sent it: http://www.acoustic.ua/forms/calculator4.en.html

You may want to experiment with position in and around the calculated values. Some ideas below on holding the panels in place for listening tests.

If you want to go cheap, I have used something like this to hold things against the ceiling when I don’t have helping hands, or I don’t want someone standing in the way of the sound. The trick is to fully extend it just slightly off vertical (so it is slightly longer than the distance to the floor), lock it, then push the base towards vertical so it has enough pressure hold whatever you are trying to hold in place. https://www.amazon.com/Mr-LongArm-3212-Pro-Pole-Extension/dp/B00004YUPO/ref=sr_1_8?keywords=extensio...

If you want to get a bit more sophisticated, https://www.amazon.com/FastCap-Support-System-144-Inches-3HAND5/dp/B000067S12/ref=sr_1_12?keywords=d... is even better. Well worth the $70 for a set of two. You can hold an acoustic panel in place with one on each corner.

Thanks @atdavid. Very helpful