  We study loop corrections to positivity bounds on effective field theories in
the context of $2\to 2$ scattering in gravitational theories, in the presence
of light particles. It has been observed that certain negative contributions at
low energies are enhanced by inverse powers of a small mass $m$ and are
nontrivial to cancel against other low-energy contributions. These originate
from near the forward limit of diagrams involving graviton exchange. We observe
that scattering in this kinematics domain remains infrared-sensitive even at
high center-of-mass energy. By considering a string-inspired model in which
high-energy loops can be calculated using unitarity and Regge behavior of tree
amplitudes, we uncover a natural mechanism through which $1/m$-enhanced terms
perfectly cancel between low and high energy contributions. This concretely
explains possible positivity violations in the presence of gravity from the
high-energy viewpoint.
