I'm installing a 7.2/3 set up in a 20x16x9 room. I'm using my trusty Monitor Audio Silver set up. I was using the Monitor Audio in ceiling speakers for my last house as rear surrounds. They have their own MDF box and sound unbelievable for in walls. But I decided to buy the MA Silver SfX surrounds:

http://www.monitoraudio.co.uk/product.php?application=&range=6&product=48&area=2

and want to know where on the side walls to mount them. I was thinking in between the front and rear seat rows. Is there a general rule?? Also, how high should they be?

If I use a 12" riser, and the ceiling is 9' where the ceiling is, we'll be sitting about 4.5-5' high (3.5'-4' average torso + 12" platform).

Should they be at or above ear level (in my case, about 5' high)? Is it a taste thing? If all else fails, I'll go with 6' and live with it. It can't be that bad.

Generally in a single row configuration they should be mounted between 90 and 110 degrees behind the listening position. When running two rows the consensus seems to be mid way between the first and second row. I placed mine closer to the first than the second as the first row gets a lot more use. As far as height 3-4 ft above the listening position seems to be the norm. I personally would experiment and see what sounds best to you.

Tweeters 24" above seated ear level is a good choice.

THX states 2' and above so McCall is right on. Us Axiom guys run them 3-4' as they are a quadpolar speaker. As mentioned I would experiment to see which suits you best.