Adjacent irregular buildings with insufficient separation are vulnerable to seismic pounding, particularly when plan asymmetry and soil flexibility modify their dynamic response. This study investigates the influence of horizontal plan layout on the seismic response and pounding behavior of adjacent irregular steel buildings considering soil–structure interaction. Six adjacent L-shaped building configurations with identical structural properties but different plan arrangements were modeled in SeismoStruct. Nonlinear time-history analyses were performed using nine real earthquake records with different intensity, duration, and frequency characteristics. Pounding was represented through nonlinear gap elements, while soil flexibility was simulated using an equivalent spring–dashpot soil–structure interaction model. The response was evaluated in terms of natural frequencies, roof displacement histories, torsional rotations, relative gap response, storey drifts, shear forces and bending moments. The results show that plan layout strongly affects global response and pounding potential. Layouts with less favorable mass and stiffness distribution produced larger roof displacements, amplified torsional rotations and higher relative gap demands. Layouts 1 and 6 generally exhibited the most critical responses, whereas Layouts 3 and 4 showed comparatively more stable behavior. The findings indicate that pounding risk is governed not only by translational displacement but also by asynchronous torsional response.