diff --git a/__init__.py b/__init__.py
index cb259db..941c932 100644
--- a/__init__.py
+++ b/__init__.py
@@ -1,31 +1,33 @@
 # Shim for submodule usage in Squid
 # Re-exports from the nested ndviewer_light package
-from .ndviewer_light import (
-    __version__,
-    FPATTERN,
-    FPATTERN_OME,
-    MAX_3D_TEXTURE_SIZE,
-    LightweightMainWindow,
-    LightweightViewer,
-    data_structure_changed,
-    detect_format,
-    extract_ome_physical_sizes,
-    read_acquisition_parameters,
-    read_tiff_pixel_size,
-    wavelength_to_colormap,
-)
+# Only imports when used as a submodule (has parent package)
+if __package__:
+    from .ndviewer_light import (
+        __version__,
+        FPATTERN,
+        FPATTERN_OME,
+        MAX_3D_TEXTURE_SIZE,
+        LightweightMainWindow,
+        LightweightViewer,
+        data_structure_changed,
+        detect_format,
+        extract_ome_physical_sizes,
+        read_acquisition_parameters,
+        read_tiff_pixel_size,
+        wavelength_to_colormap,
+    )
 
-__all__ = [
-    "__version__",
-    "FPATTERN",
-    "FPATTERN_OME",
-    "MAX_3D_TEXTURE_SIZE",
-    "LightweightMainWindow",
-    "LightweightViewer",
-    "data_structure_changed",
-    "detect_format",
-    "extract_ome_physical_sizes",
-    "read_acquisition_parameters",
-    "read_tiff_pixel_size",
-    "wavelength_to_colormap",
-]
+    __all__ = [
+        "__version__",
+        "FPATTERN",
+        "FPATTERN_OME",
+        "MAX_3D_TEXTURE_SIZE",
+        "LightweightMainWindow",
+        "LightweightViewer",
+        "data_structure_changed",
+        "detect_format",
+        "extract_ome_physical_sizes",
+        "read_acquisition_parameters",
+        "read_tiff_pixel_size",
+        "wavelength_to_colormap",
+    ]
diff --git a/ndviewer_light/core.py b/ndviewer_light/core.py
index aad2e05..0bb076e 100644
--- a/ndviewer_light/core.py
+++ b/ndviewer_light/core.py
@@ -57,6 +57,17 @@ def _patched_setRange(self, a, b):
                 if hasattr(self, "_slider"):
                     self._slider.setMinimum(a)
                     self._slider.setMaximum(b)
+
+                    # Proportional handle sizing based on number of positions
+                    num_positions = b - a + 1
+                    # Scale handle: larger for fewer positions, smaller for many
+                    # Clamp between 8px (minimum usable) and 40px (maximum reasonable)
+                    handle_width = max(8, min(40, 200 // max(1, num_positions)))
+                    self._slider.setStyleSheet(
+                        f"QSlider::handle:horizontal {{ width: {handle_width}px; }}"
+                        f"QSlider::handle:vertical {{ height: {handle_width}px; }}"
+                    )
+
                 if hasattr(self, "_label"):
                     try:
                         self._label.setRange(a, b)
diff --git a/pyproject.toml b/pyproject.toml
index ac5e657..6e88bf0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,3 +24,9 @@ dependencies = [
 [tool.setuptools.packages.find]
 where = ["."]
 include = ["ndviewer_light"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+norecursedirs = ["__pycache__"]
+addopts = "--ignore=__init__.py"