Existence/classification of Arthur-type representations from smooth-closure, non-open/non-closed orbits

Determine whether there exist non-open and non-closed H-orbits C in Vogan varieties whose closures \bar{C} are smooth such that, for some irreducible H-equivariant local system L on C, the representation π(C, L) is of Arthur type for the quasi-split form of G; if such representations exist, classify them.

Background

The authors observe that many lemmas used for open orbits still hold when orbit closures are smooth, prompting speculation about broader representation-theoretic implications. They highlight examples where Arthur-type representations correspond to open or closed orbits or to orbits with singular closure, but raise uncertainty for smooth-closure orbits that are neither open nor closed.

This question seeks to understand whether smoothness of closures implies non-Arthur type outside the extremal cases or whether exceptions exist; a classification would refine the relationship between geometric orbit properties and Arthur-type phenomena.