No, you’re doing that from within the material editor; which isn’t what I’m talking about(I can tell from the yellow undo arrow next to it). As far as I know, it’s just resampling something that has already been resampled. For example: If the version in the texture editor were set to BC1, you drag/dropped that into the material and then you set the material sampler type to BC4, the real texture would be compressed into BC1 and from that BC1, you’d now make the BC4. Now like I said, I could be entirely wrong about this, but I’m pretty sure that this is how it works. If someone has intimate knowledge of this process, please correct me if I’m wrong.
Change the textures within the actual texture editor and drop that into the material. And yes, green channel is usually the least compressed out of the bunch because our eyes see differences in it strongly.
EDIT: Oh and speaking of the green channel stuff, make sure that sRGB is turned off in the texture as well.