Texture mip map streaming only works on _MainTex?

I am using both shadergraph and writing custom fragment shaders but I cant get texture streaming to work on anything other than "_MainTex" ( Doesnt work on things like emission textures or anything else it could be used for )

There seems to be no documentation on this, if i rename _MainTex to _MainTex2 it also stops working. So I assume unity only checks for _MainTex ?

Can someone from unity give an answer on this.

Unity 2021.1

EDIT: I am debugging this via the scene view setting, renderers go blue with _MainTex is removed or renamed.