  We build on a recent result stating that the frame $\mathsf{SE}(L)$ of
strongly exact filters for a frame $L$ is anti-isomorphic to the coframe
$\mathsf{S}_o(L)$ of fitted sublocales. The collection $\mathsf{E}(L)$ of exact
filters of $L$ is known to be a sublocale of this frame. We consider several
other subcollections of $\mathsf{SE}(L)$: the collections
$\mathcal{J}(\mathsf{CP}(L))$ and $\mathcal{J}(\mathsf{SO}(L))$ of
intersections of completely prime and Scott-open filters, respectively, and the
collection $\mathsf{R}(L)$ of regular elements of the frame of filters. We show
that all of these are sublocales of $\mathsf{SE}(L)$, and as such they
correspond to subcolocales of $\mathsf{S}_o(L)$, which all turn out to have a
concise description. By using the theory of polarities of Birkhoff, one can
show that all of the structures mentioned above enjoy universal properties
which are variations of that of the canonical extension. We also show how some
of these subcollections can be described as polarities and give three new
equivalent definitions of subfitness in terms of the lattice of filters.
