I remember hearing once that the blue channel has the most compression with DXT, so that’s why you always stick AO on that one, but outside of that you should be fine sticking whatever you want in R and G. Even then, I might be wrong, it’s been a while. The best way to check is just to open a texture in Unreal and look at the channels one by one to see if there’s any notable compression artifacts, as long as it looks good then you’re probably fine.