Surface roughness, such as forward-facing steps (FFS), significantly impacts the laminar-turbulent transition in swept-wing boundary layers. This study employs direct numerical simulations (DNS) to investigate the non-monotonic relationship between FFS height and transition location, complementing recent experimental findings. Two step heights and a baseline clean surface are analyzed under experimentally representative conditions. The simulations confirm a delay in transition for the shallow FFS and premature transition for the higher FFS, reproducing experimental trends while revealing some discrepancies in the abruptness of transition advancement for the larger step. DNS results provide detailed insights into the interaction of crossflow modes with the FFS, particularly near the step, highlighting the spanwise modulation and the formation of reverse flow regions.