Just so I'm clear, here's the other way of looking at it. 3 creatures of CR 1/3 come out to EL 1. So if individual CR goes up by +1, the group is now EL 2. Thus, individual CR is really 2/3, closest to 1/2.
Similarly, an adjustment of CR +1 is really saying one "bump" up the CR scale, and the one above CR 1/3 is CR 1/2.
Again, whenever I'm confronted by this issue I look at the final creature and make a specific adjudication on it. Feel free to post the actual templated creature. Could be 1 or 1/2.