Acoustic panels on ceiling

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 

I measured from the speaker face to my  listening position by using plumb lines to place tacks in the ceiling, ran string through then, creating the angles, then made the center of the panels halfway the distance. 
See my system pics for details. They hang about 10" from the ceiling (9 foot ceiling in this space) 

Thanks @bimmerman2 ! 
Very nice system by the way. Gorgeous looking room too