I’m not sure what to think about this. On the one hand knockback is actually considered to be “better” than knockdown, so when you slot a KB-to-KD IO you’re technically spending a slot to make the power weaker. I also never really liked having to use a slot for that, because any power that you want to convert to knockdown has to make do with 5 slots. On the other hand, unlike knockback, fear effects are usually an intentional downside to the powers that have them, so maybe having to spend slots to reduce them would be more balanced? I don’t know.