diff --git a/modules/sparse_ref_panel.py b/modules/sparse_ref_panel.py
index 0ce7ced..6faecb2 100644
--- a/modules/sparse_ref_panel.py
+++ b/modules/sparse_ref_panel.py
@@ -107,14 +107,14 @@ def __getitem__(self, key: Tuple[Union[int, list, slice]]) -> sparse.csc_matrix:
                     ]
                 )
             row_stop = (
-                min([key[0].stop, self.n_variants - 1])
+                min([key[0].stop, self.n_variants])
                 if key[0].stop is not None
-                else self.n_variants - 1
+                else self.n_variants
             )
             chunks = list(
                 range(
                     (key[0].start or 0) // self.chunk_size,
-                    row_stop // self.chunk_size + 1,
+                    (row_stop - 1) // self.chunk_size + 1,
                     chunk_step,
                 )
             )
@@ -123,16 +123,19 @@ def __getitem__(self, key: Tuple[Union[int, list, slice]]) -> sparse.csc_matrix:
 
             if len(chunks) == 1:
                 return self._load_haplotypes(chunks[0])[
-                    key[0].start
-                    % self.chunk_size : row_stop
-                    % self.chunk_size : key[0].step,
+                    key[0].start % self.chunk_size : row_stop % self.chunk_size
+                    or self.chunk_size : key[0].step,
                     key[1],
                 ]
 
             slices = (
                 [slice(key[0].start % self.chunk_size, None, key[0].step)]
                 + [slice(None, None, key[0].step)] * (len(chunks) - 2)
-                + [slice(None, row_stop % self.chunk_size, key[0].step)]
+                + [
+                    slice(
+                        None, row_stop % self.chunk_size or self.chunk_size, key[0].step
+                    )
+                ]
             )
             return sparse.vstack(
                 [
@@ -238,7 +241,7 @@ def _load_sample_ids(self) -> List[str]:
             print(f"An error occurred: {str(e)}")
             return []
 
-    def determine_start_position(self, vcf_path) -> int:
+    def _determine_start_position(self, vcf_path) -> int:
         cmd = f'bcftools query -f "%POS\n" {vcf_path} | head -1'
         result = subprocess.run(
             cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True, shell=True
@@ -247,12 +250,12 @@ def determine_start_position(self, vcf_path) -> int:
             raise ValueError(f"Error executing bcftools: {result.stderr}")
         return int(result.stdout.strip())
 
-    def determine_chunk_ranges(self, vcf_path, chr_length, num_variants):
+    def _determine_chunk_ranges(self, vcf_path, chr_length, num_variants):
         chr_length = int(chr_length)
         num_variants = int(num_variants)
         bp_per_variant = chr_length / num_variants
         bp_per_chunk = bp_per_variant * self.chunk_size
-        current_start = self.determine_start_position(vcf_path)
+        current_start = self._determine_start_position(vcf_path)
         ranges = []
         while current_start < chr_length:
             end = min(current_start + bp_per_chunk, chr_length)
@@ -263,7 +266,7 @@ def determine_chunk_ranges(self, vcf_path, chr_length, num_variants):
         ranges[-1] = (ranges[-1][0], 999_999_999)
         return ranges
 
-    def get_vcf_stats(self, vcf_path):
+    def _get_vcf_stats(self, vcf_path):
         cmd = ["bcftools", "index", "--stats", vcf_path]
         result = subprocess.run(
             cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True
@@ -279,8 +282,8 @@ def get_vcf_stats(self, vcf_path):
         return chrom, chr_length, num_variants
 
     def _ingest_variants(self, vcf_path: str, threads: int = os.cpu_count()):
-        chrom, chr_length, num_variants = self.get_vcf_stats(vcf_path)
-        chunk_ranges = self.determine_chunk_ranges(vcf_path, chr_length, num_variants)
+        chrom, chr_length, num_variants = self._get_vcf_stats(vcf_path)
+        chunk_ranges = self._determine_chunk_ranges(vcf_path, chr_length, num_variants)
 
         def process_chunk(args):
             start, end, chrom, vcf_path = args