At some point, someone (Goku or Vegeta) said they would outdo their SSJ self. The way that was worded, I interpret it this way: To make their base level higher than the additive boost they get as SSJs. If the SSJ boost is 150 mil, then when someone's base level exceeds 150 mil, they outdo their SSJ self in their base form, and only then can they ascend to the grade forms. What do you think?