For 5.1 channel home theater speaker systems, a good location for surround effects speakers is perpendicular to the left and right sides of your prime home theater seating area, either mounted high up on the walls or ceiling, or secured atop tall floor stands.

Bipolar and dipolar surround speakers do the best job of creating a diffuse sense of ambient spaciousness and envelopment that's similar to what you experience when you go see a movie at the local digital cinema.

For more directional rear surround sound effects, you could instead choose to go with a pair of voice-matched (from the same manufacturer and series) bookshelf or satellite speakers, either mounted or on stands.