  Smearing the bare quantum fields in lattice calculations before applying
composite hadron creation operators has a long record of substantially
improving overlaps onto low-lying energy eigenstates. A technique called
distillation which defines smearing for quark fields as a low-rank linear
projection operator into a small vector space of smooth gauge-covariant fields
has proven to be both effective and versatile in hadron spectroscopy
calculations albeit with significant computational cost . In this paper, more
general operators in this space of smooth fields are introduced and optimised,
which enhances the performance of the method when tested on systems of heavy
quark-anti-quark pairs close to the charmonium energy scale.
