diff --git a/include/ck_tile/ops/fmha/block/block_masking.hpp b/include/ck_tile/ops/fmha/block/block_masking.hpp
index 61d22f7e2b..51a5952d2f 100644
--- a/include/ck_tile/ops/fmha/block/block_masking.hpp
+++ b/include/ck_tile/ops/fmha/block/block_masking.hpp
@@ -283,11 +283,12 @@ struct SimplifiedGenericAttentionMask
     }
     CK_TILE_HOST_DEVICE
     SimplifiedGenericAttentionMask(
-        index_t y_, index_t x_, index_t y_total_, index_t x_total_, mdiv y_ratio_mdiv_)
-        : y(y_),
+        index_t y_real_, index_t x_, index_t y_total_, index_t x_total_, mdiv y_ratio_mdiv_)
+        : y(y_real_ * static_cast<index_t>(y_ratio_mdiv_.get())),
           x(x_),
           y_total(y_total_),
           x_total(x_total_),
+          y_real(y_real_),
           y_ratio(static_cast<index_t>(y_ratio_mdiv_.get())),
           y_ratio_mdiv(y_ratio_mdiv_)
     {
@@ -335,10 +336,9 @@ struct SimplifiedGenericAttentionMask
             {
                 // get the tile start/end range assum we loop over along X tile by tile
                 index_t x_start = [&]() {
-                    index_t tmp_offset = -y + i_y + y_ratio;
-                    index_t tmp_div =
-                        static_cast<index_t>(y_ratio_mdiv.div(static_cast<uint32_t>(tmp_offset)));
-                    index_t tmp = tmp_offset > 0 ? tmp_div : 0; // clamp by zero
+                    index_t tmp =
+                        -y_real +
+                        static_cast<index_t>(y_ratio_mdiv.div(static_cast<uint32_t>(i_y))) + 1;
 
                     return (tmp / XTile) * XTile; // round to tile aligned
                 }();
@@ -443,13 +443,9 @@ struct SimplifiedGenericAttentionMask
             }
             else
             {
-                index_t start_tmp = -y + i_y + y_ratio;
-                index_t start_tmp_div =
-                    static_cast<index_t>(y_ratio_mdiv.div(static_cast<uint32_t>(start_tmp)));
-                index_t x_start = start_tmp > 0 ? start_tmp_div : 0; // clamp by zero
-
-                uint32_t end_tmp = static_cast<uint32_t>(i_y);
-                index_t x_end    = min(static_cast<index_t>(y_ratio_mdiv.div(end_tmp)) + x,
+                index_t x_tmp = static_cast<index_t>(y_ratio_mdiv.div(static_cast<uint32_t>(i_y)));
+                index_t x_start = -y_real + x_tmp + 1;
+                index_t x_end   = min(x_tmp + x,
                                     x_total); // need min in case x is padded
                 return i_x < x_start || i_x >= x_end || i_y >= y_total;
             }
@@ -504,7 +500,9 @@ struct SimplifiedGenericAttentionMask
     private:
     index_t y, x;
     index_t y_total, x_total;
-    index_t y_ratio = 1;
+    // y_real is vertical axis before multiplying y_ratio. y_real * y_ratio = y
+    index_t y_real;
+    index_t y_ratio;
     mdiv y_ratio_mdiv;
 };