Stephen,
In each case the tube was from a kitchen roll around 43mm diameter.
I need to remind myself of your original perhaps you can post it here. I am sure this would be more versatile 130mm plays 500mm.
I have just tried zooming the 1 1/2 inch section inside a toilet roll ( just over 4 1/4 long ) and it has no real effect on the light pattern.
This suggests that straw length inside the tube determines the diameter of the projected light.
Don
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