Not a definitive answer - yet possibly an answer.

Assuming you're using EnergyPlus (although comparable engines would likely behave similarly), differences in results could come from reduced solar-ground reflections in Scenario 1. Both sky and beam solar contributions, diffusively reflected from the ground towards receiving surfaces, are is diminished (vs Scenario 2). You could look into detailed output, or simply tweak the site ground reflectance for a quick assessment.