[en] Using a non-relativistic model we compute the response of symmetric nuclear matter and find that final state interaction effects become negligible for momentum transfers q> or approx.(0.6-0.7)m. This indicates that for moderate energy losses, nuclear matter becomes asymptotically free beyond the onset, but not deep into the relativistic regime. We then assess the importance of off-shell effects in the binary collision t-matrix and show that on-shell approximations approach the off-shell response only for q> or approx.2 GeV. Next we argue that V_opt cannot generally replace the interaction of the recoiling particle with the medium. Finally we show that for fixed q the response decreases exponentially as function of a scaling variable γ, if the imaginary part of the high-q elastic amplitude dominates. (orig.)