I know that the amino group $\ce{-NH2}$ is a strong activator, so the sulfonate group $\ce{-SO3H}$ should be directed at the ortho or para position. However, the sulfonation occurs at para position on the adjacent ring:
Why is that and what effect does the amino group have on the reaction?
![Aromatic sulfonation of [1,1'-biphenyl]-3-amine to 3'-amino-[1,1'-biphenyl]-4-sulfonic acid](../../images/2d7537a33230269cd8640f796f20824a.webp)