What about this? It takes basically the same amount of space because the "Slice" property already had its own line, and it's much more explicit about the hierarchy of options.

Code:

class DATA_PT_volume_viewport_display_slicing(DataButtonsPanel, Panel):
    bl_label = ""
    bl_parent_id = "DATA_PT_volume_viewport_display"
    COMPAT_ENGINES = {'BLENDER_RENDER', 'BLENDER_EEVEE', 'BLENDER_WORKBENCH'}

    def draw_header(self, context):
        layout = self.layout

        volume = context.volume
        display = volume.display

        layout.prop(display, "axis_slice_method")

    def draw(self, context):
        layout = self.layout
        layout.use_property_split = True
        layout.use_property_decorate = False

        volume = context.volume
        display = volume.display
        
        layout.active = display.axis_slice_method
        
        col = layout.column()
        col.prop(display, "slice_axis")
        col.prop(display, "slice_depth")

What about this? It takes basically the same amount of space because the "Slice" property already had its own line, and it's much more explicit about the hierarchy of options.

I agree that is much better.

@Hans Goudey (HooglyBoogly) Yes, a sub-panel for slicing options brings so much more clarity. Will incorporate that for Volume Object.
For the same in fluid, placing the 'Slice Per Voxel' slider would be tricky as it should be usable only when single-slicing is disabled.

In D9097#224176, @Sriharsha Kotcharlakot (Sriharsha) wrote:

@Hans Goudey (HooglyBoogly) Yes, a sub-panel for slicing options brings so much more clarity. Will incorporate that for Volume Object.
For the same in fluid, placing the 'Slice Per Voxel' slider would be tricky as it should be usable only when single-slicing is disabled.

That's fine, just put "Slice Per Voxel" above the subpanel and gray it out when "use_slice" is on with col.active.

In D9097#224249, @Hans Goudey (HooglyBoogly) wrote:

In D9097#224176, @Sriharsha Kotcharlakot (Sriharsha) wrote:

@Hans Goudey (HooglyBoogly) Yes, a sub-panel for slicing options brings so much more clarity. Will incorporate that for Volume Object.
For the same in fluid, placing the 'Slice Per Voxel' slider would be tricky as it should be usable only when single-slicing is disabled.

That's fine, just put "Slice Per Voxel" above the subpanel and gray it out when "use_slice" is on with col.active.

Ah right, will do that, thanks