Why does the "Island Margin" value have barely any effect when using Smart UV Project

As the title says, it is easy to see the effect of the margin when using regular unwrap or doing a Lightmap Pack, but it barely has any effect when you crank it up to 1 with Smart UV Project.

I see a significant effect with a demo object (unwrapped with Smart UV Project)

Show us what you mean

i attached the blend file and the pictures below show the difference between 0 and 1. thanks for looking

lavatory.blend (1.72 MB)