  We discuss the limitations of the covariant derivative expansion prescription
advocated to compute the one-loop Standard Model (SM) effective lagrangian when
the heavy fields couple linearly to the SM. In particular, one-loop
contributions resulting from the exchange of both heavy and light fields must
be explicitly taken into account through matching because the proposed
functional approach alone does not account for them. We review a simple case
with a heavy scalar singlet of charge $-1$ to illustrate the argument. As two
other examples where this matching is needed and this functional method gives a
vanishing result, up to renormalization of the heavy sector parameters, we
re-evaluate the one-loop corrections to the T--parameter due to a heavy scalar
triplet with vanishing hypercharge coupling to the Brout-Englert-Higgs boson
and to a heavy vector-like quark singlet of charged $2/3$ mixing with the top
quark, respectively. In all cases we make use of a new code for matching
fundamental and effective theories in models with arbitrary heavy field
additions.
