below, at higher and higher laser intensities the distance covered by the virtual electron and positron before annihilating decreases accordingly, in such a way that the process occurs with a net exchange of a low number of laser photons. This is in contrast, as we have mentioned, to the NBWPP, which is also primed in the collision of a (real) photon and a laser field. However, in NBWPP the final electron and positron are on the mass shell, requiring a large amount of laser photons to be absorbed for the process to occur at all in the presence of an ultra-relativistic laser field. Although the analysis is limited to the one-loop amplitude of a refractive QED effects and does not cover observable quantities as cross-sections or rates, the present results can be of relevance for future experimental campaigns, aiming to measure strong-field QED effects in the presence of a background laser field. As we will see, they indicate, for example, that, in order to detect refractive QED effects in a regime where higher-order effects in the laser-field amplitude are important, it is more convenient to measure the yield of final photons, rather than to measure the angular distribution or the 