In this paper we develop a technique for proving determinacy of classes of the form ω²-Π¹₁+Γ (a refinement of the difference hierarchy on Π¹₁ lying between ω²-Π¹₁ and (ω²+1)-Π¹₁) from weak principles, establishing upper bounds for the determinacy- strength of the classes ω²-Π¹₁+Σ^0_α for all computable α and of ω²-Π¹₁+Δ¹₁. This bridges the gap between previously known hypotheses implying determinacy in this region.