  In these proceedings we investigate the impact of offshell and non-resonant
contributions to kinematic distributions in $t\bar{t}$ final states by
comparing several next-to-leading-order~(NLO) + parton shower (PS) generators
which differ in the way they model these effects. We focus on distributions
traditionally used for measurements of fundamental top-quark properties such as
its Yukawa coupling or its mass. Given the current experimental uncertainties,
we find that such effects can have relatively large impact on the shape of
these distributions and are thus mandatory for accurate measurements.
