In any case, self defense aspects also involve concealment, and thus fairly small knives. As we shall see, where throwing knives are concerned, small is not necessarily beautiful. The only thing balance determines is the knife's suitability as a handle vs. a blade thrower. A knife that is handle heavy, throws more easily when gripped from the blade. Only knives that are balanced very close to their center point can be thrown equally well from handle or blade.
Length is important because a longer knife turns more slowly.
This is good. It means that the knife will travel further horizontally for every turn or fraction of a turn it makes. In practical terms, it means that for any given throw, the knife will stick in the target over a wider throwing distance. That is, the difference between being too close and being too far grows larger as the knife gets longer. Weight is important for control and momentum.