Well, it's a good point no? If the universe is expanding as the photons propagate they are spread out into that larger sphere. So for the purposes of light gathering, a galaxy 13 billion years in the past has its photons spread over that much larger sphere into even greater invisibility. Although I guess in this case they were spread out into the larger sphere at the point of the expansion of the universe of a few billion years ago before being focused towards us - so. Some value significantly smaller than 46 but a lot larger than 10. Which makes it even more amazing to think about.
I just ate a bunch of food. I am now more massive. So I have stretched space around me a bit more than I did before I ate. You just need to make an instrument sensitive enough to detect it.
The radius of the universe is irrelevant.