In this case, you're on a decent length approach and you'll likely to be looking forward as you approach the limit line. If you're going to see a sign across 3 lanes on the center island, the likelihood is that you WILL see the sign in its current location. Then you're expected to stop at the limit line (as you suggested), start rolling forward to clear traffic and as you do, you're most likely to look left first, then look right and then maybe left again as you enter the roadway, -you still haven't looked "forward" again since before the stop-. So that might seem like it is an ideal location, but... is it really?
Of course the CVC only requires "ONE" sign and that requirement has been met!