hair thickness vs spot size

So if smaller spot size/higher joules/lower pulse is good for thinner hair, what does it do for thicker hair. My guess is not penetrate deep enough to kill it.
Is this the theory behind diminishing returns. Large spot with max settings for other variables makes hair thinner until they can use higher joules with the smaller spot? Hope that made sense <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

diminishing returns means that as hair gets finer (or remaining hair that can’t be targeted by laser anymore because it doesn’t have enough pigment), there is a point where you’re using max joules and smaller spot size combination but the hairs still don’t have enough pigment because they’re too fine at that point. Btw, shorter pulse is more effective. I’m not sure if that’s what you meant.