Strange IOR behavior

[Tetsuoo]

Hi,
It's been post on Youtube but I think I should post here as well. I can't really say I "need help" but this was bugging me somehow.
I discovered that by chance, it seems that even with Refraction set to 0, the IOR value still have an effect on a material using SSS and translucency.
I know, it doesn't make sense so here I reproduced the problem and made a screenshot of it

[maru]

It looks like it could be by design. I just recalled adding this to the SSS guide: https://coronarenderer.freshdesk.com/support/solutions/articles/5000534910

Refraction IOR affects translucency

But it would be great if Ondra could confirm this.

update: explained below

[Ondra]

it affects things in a very subtle way: reflection IOR is calculated using the fresnel IOR in reflection tab ONLY when ENTERING medium. When LEAVING a medium, the refraction IOR is always used. This was necessary to prevent some very prominent artifacts when using some wild combinations of reflect and refract IOR.

[Ludvik Koutny]

Yep, basically refraction IOR affects Fresnel reflection on those faces on the inside.

[Tetsuoo]

Alright, still a bit strange in my head but I think I get it. I guess it's not possible/logical not having refraction while having translucency at the same time. And reflections.
So, what's your advice guys, keep Refraction IOR and Reflection IOR the same value ?

[Ondra]

So, what's your advice guys, keep Refraction IOR and Reflection IOR the same value ?

yes, if you have no specific reason to set them differently, keep them same

[Tetsuoo]

Thank you.