i think they call it surround speakers and surround back, probably the only reason why people are calling it side surround is becuase it is placed at the side wall but my undertansding is that you only have a surround and surround back/rear surround speaker.
if you intend to use your bipole as surround back speaker, you need to change the assignment in the receiver accordingly. my take is that if Im using a dipole speaker, the value of installing a surround back would not be that significant anymore, similar if im using a bipole. the surround back speaker provides the least impact as most of the time monopole speakers are used for this purpose at least based on my own experience
the front wide speakers created the most impact in my set up before though there are some people who says the front height serves them better than the front wide does. there is a mounting requirement for these speakers and ensuring this is observed will create the optimum listening experience.