  The A-model for finite rank singular perturbations of class
$\mathfrak{H}_{-m-2}\smallsetminus\mathfrak{H}_{-m-1}$, $m\in\mathbb{N}$, is
considered from the perspective of boundary relations. Assuming further that
the Hilbert spaces $(\mathfrak{H}_n)_{n\in\mathbb{Z}}$ admit an orthogonal
decomposition $\mathfrak{H}^-_n\oplus\mathfrak{H}^+_n$, with the corresponding
projections satisfying $P^\pm_{n+1}\subseteq P^\pm_n$, nontrivial extensions in
the A-model are constructed for the symmetric restrictions in the subspaces.
