How UI Batching works with two different sprites ?

Hi there,

I'm working on UI, and I'm facing a problem of comprehension :

I have two Image with different sprite (but sprites are from the same sprite pack), I display them in a canvas set in World Space mode : 2 batches. Overlapped or not.

Why ? I read a PDF from Tim Cooper for an Asian presentation of how UI Batching works. I followed every steps : Same material, same texture (because it's in the same sprite packer), it's coplanar to the canvas, ... What do i miss ?

Batching works because if I put the same sprite on the two Image components, I got 1 batch. But if I put another sprite (but still from the same sprite pack), editor show me 2 batches.

Can someone helps or explain this ?

Thanks a lot community ! :)