Spectator-induced electromagnetic (EM) effects in light- and heavy ion collisions provide information on the space-time evolution of the system of hot and dense matter created at high energy. Numerical simulations of such effects necessitate, as a component of key importance, proper initial double differential distributions of the emitted charged particles under study in a very large (preferably complete) area of phase space. The phenomenological construction of such distributions imposes a significant challenge, in particular if at a given collision energy the experimental information remains incomplete in terms of coverage. This talk will present the results of such an effort for the relatively difficult case of c.m.s. collision energy √sNN=8.8 GeV, where on the one hand, model-independent extrapolations must be performed in the high xF regime particularly sensitive to EM effects, and on the other hand, strong deviations from Feynman scaling in the central region must be precisely evaluated as a function of simultaneously xF and pT. The results of this work can be directly applied to phenomenological studies of new experimental data on EM effects in Ar+Sc collisions, obtained by the NA61/SHINE experiment at the CERN SPS.
