diff --git a/daft/runners/ray_runner.py b/daft/runners/ray_runner.py
index f0dfc5259c..898a1f2207 100644
--- a/daft/runners/ray_runner.py
+++ b/daft/runners/ray_runner.py
@@ -1502,8 +1502,8 @@ def push_based_shuffle_service_context(
         num_cpus = int(ray.cluster_resources()["CPU"])
 
         # Number of mappers is ~2x number of mergers
-        num_map_tasks = num_cpus // 3
-        num_merge_tasks = num_map_tasks * 2
+        num_merge_tasks = num_cpus // 3
+        num_map_tasks = num_merge_tasks * 2 + (num_cpus % 3)
 
         yield RayPushBasedShuffle(num_map_tasks, num_merge_tasks, num_partitions, partition_by)
 
@@ -1570,7 +1570,7 @@ def _get_reducer_inputs_location(self, reducer_idx: int) -> tuple[int, int]:
             if num_reducers > reducer_idx:
                 return merger_idx, reducer_idx
             else:
-                reducer_idx - num_reducers
+                reducer_idx -= num_reducers
         raise ValueError(f"Cannot find merger for reducer_idx: {reducer_idx}")
 
     def _merger_options(self, merger_idx: int) -> dict[str, Any]:
@@ -1613,25 +1613,24 @@ def run(self, materialized_inputs: list[ray.ObjectRef]) -> list[ray.ObjectRef]:
         Each Mapper then should run partitioning on the data into `N` chunks.
         """
         # [N_ROUNDS, N_MERGERS, N_REDUCERS_PER_MERGER] list of outputs
-        merge_results: list[list[list[ray.ObjectRef]]] = []
+        total_merge_results: list[list[list[ray.ObjectRef]]] = []
         map_results_buffer: list[ray.ObjectRef] = []
 
         # Keep running the pipeline while there is still work to do
         while materialized_inputs or map_results_buffer:
             # Drain the map_results_buffer, running merge tasks
             per_round_merge_results = []
-            while map_results_buffer:
-                map_results = map_results_buffer.pop()
-                assert len(map_results) == self._num_mergers
-                for merger_idx, merger_input in enumerate(map_results):
+            if map_results_buffer:
+                for merger_idx in range(self._num_mergers):
+                    merger_input = [mapper_results[merger_idx] for mapper_results in map_results_buffer]
                     merge_results = merge_fn.options(
                         **self._merger_options(merger_idx), num_returns=self._num_reducers_for_merger(merger_idx)
                     ).remote(*merger_input)
                     per_round_merge_results.append(merge_results)
-            if per_round_merge_results:
-                merge_results.append(per_round_merge_results)
+                total_merge_results.append(per_round_merge_results)
 
             # Run map tasks:
+            map_results_buffer = []
             for i in range(self._num_mappers):
                 if len(materialized_inputs) == 0:
                     break
@@ -1643,8 +1642,10 @@ def run(self, materialized_inputs: list[ray.ObjectRef]) -> list[ray.ObjectRef]:
                     map_results_buffer.append(map_results)
 
             # Wait for all tasks in this wave to complete
-            ray.wait(per_round_merge_results)
-            ray.wait(map_results_buffer)
+            for results in per_round_merge_results:
+                ray.wait(results)
+            for results in map_results_buffer:
+                ray.wait(results)
 
         # INVARIANT: At this point, the map/merge step is done
         # Start running all the reduce functions
@@ -1652,7 +1653,9 @@ def run(self, materialized_inputs: list[ray.ObjectRef]) -> list[ray.ObjectRef]:
         reduce_results = []
         for reducer_idx in range(self._num_reducers):
             assigned_merger_idx, offset = self._get_reducer_inputs_location(reducer_idx)
-            reducer_inputs = [merge_results[round][assigned_merger_idx][offset] for round in range(len(merge_results))]
+            reducer_inputs = [
+                total_merge_results[round][assigned_merger_idx][offset] for round in range(len(total_merge_results))
+            ]
             res = reduce_fn.options(**self._reduce_options(reducer_idx)).remote(*reducer_inputs)
             reduce_results.append(res)
         return reduce_results