ON THIS WIKI
Sensivity Boost is an enchantment to Ethereal Familiar, which will increase attack range. In order to upgrade the Familiar with a certain level, it has to be already upgraded with the previous level of enchantment.
Thaumcraft 4 Research Notes
Attacking even further
"By enhansing the wisps sensivity to external influence, you can slightly increasing its range.
Consumes additionally 0.02 Aer vis and 0.01 Ordo vis per attack and level."Aspect the Ethereal Essence is related to has to match the Aspect the Ethereal Familiar is related to and the 4th aspect in the recipe. In this article it is
Sensivity Boost I
Sensivity Boost II