  We analyze scenarios in which pairs of Unruh-DeWitt-like detectors interact
with scalar field(s) with bi-linear and quadratic coupling. For all cases --
real scalar fields, charged scalar fields, and even for couplings mixing two
different scalar fields -- we find that the detectors' dynamics depends on the
Wightman function of a real scalar field with the same functional form up to a
constant multiple. Consequently, entanglement harvesting exhibits low
sensitivity to either the kind of scalar field or their charged nature.
Furthermore, we show on general grounds that pairs of Unruh-DeWitt-like
detectors exhibit persistent divergences when they interact with scalar
field(s) with a quadratic or bi-linear coupling and discuss possible avenues to
improve the models through the regularization of such divergences.
