diff --git a/cuslines/cuda_python/cu_tractography.py b/cuslines/cuda_python/cu_tractography.py
index 7064cc9..9b539be 100644
--- a/cuslines/cuda_python/cu_tractography.py
+++ b/cuslines/cuda_python/cu_tractography.py
@@ -49,7 +49,7 @@ def __init__(
         ngpus: int = 1,
         rng_seed: int = 0,
         rng_offset: int = 0,
-        chunk_size: int = 100000,
+        chunk_size: int = 25000,
     ):
         """
         Initialize GPUTracker with necessary data.
@@ -91,6 +91,9 @@ def __init__(
         rng_offset : int, optional
             Offset for random number generator
             default: 0
+        chunk_size : int, optional
+            Number of seeds to process in each chunk per GPU
+            default: 25000
         """
         self.dataf = np.ascontiguousarray(dataf, dtype=REAL_DTYPE)
         self.metric_map = np.ascontiguousarray(stop_map, dtype=REAL_DTYPE)
@@ -252,22 +255,26 @@ def generate_sft(self, seeds, ref_img):
         )
         return StatefulTractogram(array_sequence, ref_img, Space.VOX)
 
-    # TODO: performance: consider a way to just output in VOX space directly
     def generate_trx(self, seeds, ref_img):
         global_chunk_sz, nchunks = self._divide_chunks(seeds)
 
         # Will resize by a factor of 2 if these are exceeded
         sl_len_guess = 100
-        sl_per_seed_guess = 3
+        sl_per_seed_guess = 4
         n_sls_guess = sl_per_seed_guess * seeds.shape[0]
 
         # trx files use memory mapping
+        trx_reference = TrxFile(
+            reference=ref_img
+        )
+        trx_reference.streamlines._data = trx_reference.streamlines._data.astype(np.float32)
+        trx_reference.streamlines._offsets = trx_reference.streamlines._offsets.astype(np.uint64)
+
         trx_file = TrxFile(
-            reference=ref_img,
             nb_streamlines=n_sls_guess,
             nb_vertices=n_sls_guess * sl_len_guess,
+            init_as=trx_reference
         )
-        trx_file.streamlines._offsets = trx_file.streamlines._offsets.astype(np.uint64)
         offsets_idx = 0
         sls_data_idx = 0