diff --git a/csrc/jit_kernels/heuristics/common.hpp b/csrc/jit_kernels/heuristics/common.hpp
index 3ed4d2a..681e654 100644
--- a/csrc/jit_kernels/heuristics/common.hpp
+++ b/csrc/jit_kernels/heuristics/common.hpp
@@ -152,8 +152,11 @@ static GemmConfig get_best_config(const GemmType& gemm_type, const KernelType& k
 
     // Select M/N block sizes
     // TODO: support `% 16 == 8` block size on SM90
-    const auto& block_ms = gemm_type == GemmType::MGroupedContiguous ?
-        std::vector{get_mk_alignment_for_contiguous_layout()} : std::vector{64, 128, 256};
+    auto block_ms = std::vector{64, 128, 256};
+    if (gemm_type == GemmType::MGroupedContiguous)
+        block_ms = std::vector{get_mk_alignment_for_contiguous_layout()};
+    if (gemm_type == GemmType::MGroupedMasked)  // Exclude 256 for performance
+        block_ms = std::vector{64, 128};
     std::vector<int> block_ns;
     for (int i = 16; i <= 256; i += 16)
         block_ns.push_back(i);
@@ -214,7 +217,7 @@ static GemmConfig get_best_config(const GemmType& gemm_type, const KernelType& k
     MulticastConfig best_multicast_config = {1, true};
     const auto& [is_legal_on_a, is_legal_on_b] = ArchSpec::get_multicast_legality(
         gemm_type, m, n, best_block_m, best_block_n, num_sms);
-    const bool is_legal[2] = {is_legal_on_a, is_legal_on_b};
+    const bool is_legal[2] = {is_legal_on_b, is_legal_on_a};
     bool order[2] = {false, true};
     if (best_block_m > best_block_n)
         std::swap(order[0], order[1]);
diff --git a/csrc/jit_kernels/heuristics/sm100.hpp b/csrc/jit_kernels/heuristics/sm100.hpp
index 4e58289..0679cad 100644
--- a/csrc/jit_kernels/heuristics/sm100.hpp
+++ b/csrc/jit_kernels/heuristics/sm100.hpp
@@ -91,8 +91,8 @@ struct SM100ArchSpec {
                                                       const int& num_sms) {
         // TODO: support other layouts
         return {
-            is_multicast_legal(m, block_m, 2, num_sms, true) and (gemm_type == GemmType::Normal or gemm_type == GemmType::KGroupedContiguous),
             false,
+            is_multicast_legal(m, block_m, 2, num_sms, true) and (gemm_type == GemmType::Normal or gemm_type == GemmType::KGroupedContiguous),
         };
     }
 
diff --git a/csrc/jit_kernels/heuristics/sm90.hpp b/csrc/jit_kernels/heuristics/sm90.hpp
index 16ca018..58faecf 100644
--- a/csrc/jit_kernels/heuristics/sm90.hpp
+++ b/csrc/jit_kernels/heuristics/sm90.hpp
@@ -71,7 +71,9 @@ struct SM90ArchSpec {
                                                         const int& num_sms) {
         return {
             is_multicast_legal(n, block_n, 2, num_sms, gemm_type == GemmType::MGroupedMasked),
-            is_multicast_legal(m, block_m, 2, num_sms, false) and gemm_type != GemmType::MGroupedMasked,
+            // For masked GEMM layout, divisibility on N is also required as we must ensure the total number of blocks is even
+            is_multicast_legal(m, block_m, 2, num_sms, false)
+                and (gemm_type != GemmType::MGroupedMasked or is_multicast_legal(n, block_n, 2, num_sms, true))
         };
     }