Here is what I have thought. +1 ECLs like Tiefling and Aasimar have become base level 0, so ECL +1 would be base 0 CR and ECL. ECLs +2 appear to be on par with CR 1 creatures, so effectively +1 ECL. ECL 4-5 appear to be CR 3 so effectively ECL +3. I haven't had a chance to play test the ECL 4-5.
