This study investigates the combined effects of shell spacing and loading positions on the mechanical behavior of multi-span soil-steel composite structures (SSCS) during construction and under ultimate load conditions. Nonlinear finite element analysis (FEA) using the ZSoil FEA program was employed to analyze variations in three loading positions and five different spacings between the shells. The research is based on years of experience in the analysis of such structures; it was conducted in the laboratory and during field studies and analysis of the failure mechanisms of these structures (the results of this study were discussed at previous meetings of the European Conference on Buried Flexible Steel Structures). The study explores the critical relationship between spacing (S)-to-span (D) ratios and vertical displacements at the crown and haunch of the shells under different loading conditions. Findings reveal a significant 32% decrease in load-bearing capacity under narrow spacing (S/D = 0.04) in the first loading position. Comparisons between loading positions demonstrate a minor 2% reduction in bearing capacity for the second loading position compared to the first, while the third position exhibits nearly double the bearing capacity of the first two. This research emphasizes the necessity of considering shell spacing for optimal load-bearing capacity and structural integrity in multi-span SSCS design. The insights provided are valuable for engineers and designers working on soil-steel composite structures under ultimate load conditions.