If you want ideal 7 identical monopole speakers is what should be used like under ITU/ SMPTE specs. The problem with this set up is many room sizes this won't have a good surround effect except for maybe a couple of seats if the speakers are too close to the listeners. The person sitting next to the left surround will get that speaker in the ear effect and not get the same immersion as the person in the center seat. This is also true of the rear speakers if they are too close to the listening position.
If you are using di-poles they have to follow a certain orientation. Di-poles should be labeled left and right with the in phase tweeter facing forward toward the screen. When used for back speakers they get reversed and the in phase faces toward the other back speaker. So in the back the left and right speakers are reversed. Bi-poles don't need a specific orientation. Use speakers that best fit your application monopole, di-pole or, bi-pole.