Assuming your basement is dry, no moisture problems etc. and also assuming you are talking about blanket fiberglass insulation, here is my answer. The amount of work required to put one and a half inch wide slivers of insulation behind each stud is a total waste of time. "R" value on vertical walls is actually not as important as trapping air and preventing drafts. Don't get me wrong, the more "R" the better, but the majority of heat loss is up and compromised by cold air drafts. Just install insulation between studs, you will be fine. Remember, in your case, the vapor barrier goes between the concrete and insulation, not under the drywall on top of the studs.