Recently, a set of q-series invariants, labeled by \(\operatorname {Spin}^c\) structures, for weakly negative definite plumbed 3-manifolds called the \(\widehat{Z}_a\) invariants were discovered by Gukov, Pei, Putrov and Vafa. The leading rational power of the \(\widehat{Z}_a\) invariants are invariants themselves denoted by \(\Delta _a\) . In this paper, we further analyze the structure of these \(\Delta _a\) invariants. We review some of the foundations of the \(\Delta _a\) invariants and analyze their structure for a subclass of integer homology spheres. In particular, we provide a complete description of the \(\Delta _0\) invariants for Brieskorn spheres. Along the way we show that the \(\Delta _a\) invariants are not homology cobordism invariants, thereby answering an open question in the literature.