For the AR-15 guys.Got a DPMS AR-15 awhile back and am now wanting to put a scope on it.Do most people put the scope on a riser or just straight on top.Its a flat-top with no sights at all and going to put a 3x9 on it.Looks like it would be really low just mounted without a riser but thats just me looking from the side.I have not bought any mounts yet,just scope.Any help would be appreciated.THANKS.