Should have known that you meant Electrophilic substitution reaction
The vacant orbital on the electrophile finds it easier to overlap with the p-orbitals at the peri positions (C1, C4, C5, C8). This is due to the fact that these orbitals contribute the most to the HOMO (psi 5).
The pic below is of the HOMO in naphthalene, notice the greater contribution at C1,C4,C5 & C8.