Should I use small height and rear speakers?

[soundwave628]

I'm new to the site and have been trying to read up on all sorts of things and maybe I missed the discussion on this.
I bought an onkyo HT-s6200 HTiB and have since upgraded my fronts to Polk monitor 70s, polk cs20 center and monitor 60s for surrounds. Would it improve my movie experience if I used the original onkyo fronts as my rear speakers even though my couch is up against the wall? Or will it defeat the whole purpose because the sound will be going right over my head. Should I mount them and angle them down?
Also if I do that would it make any difference if I used two of the onkyo surround speakers as front height speakers? Or will they just be drowned out by the monitor 70s because the onkyo surrounds only have one 3" driver I believe.
If the onkyos with only one 3" driver aren't worth using where would the two "front" channel onkyos be put to best use.