Speaker placement formula

I tried looking in the old threads and I didn't find what I am looking for. Hopefully this isn't a subject that has been asked about too much.

I am looking for a formula (I'm almost positive Martin Logan prints one in their manual) that calculates speaker placement in the room. It takes into account ceiling height also. I know about the whole equilateral triangle, but I think Martin Logan's is different. And if I'm not mistaking, ML's is a pretty common formula? I could be wrong. If anyone could help, that would be great. Thanks.

Seth