Question 2D texture from multiple sprite

Hello. So I have a shader that radially fills texture over 360 degrees. The texture I use is in multiple sprite mode, specifically there are 2 sprites in it. For the sprite renderer I apply the shader to I put one of the sprites into the `sprite` field. However, in the _MainTex field of the material the whole texture (i.e. entire spritesheet of 2 sprite) appears instead of the one sprite I put into the sprite renderer. How can I set _MainTex of material to the specific sprite of the sprite renderer and not the whole spritesheet texture?
Unity2019.2.0b4 LWPR 2DUnlit