I got interested in this problem of the sun's reflection so I cracked the old physics book and went to the optics section.
It might seem that the sun's reflection should appear like a luminescent quarter glued to the helmet but this is incorrect.
What you see in the reflection is a virtual image appearing to originate somewhere behind the mirror. In the case of the sun and the astronaut, the sun's image will appear behind the visor, at a distance of half the radius of curvature of the visor. Its simple equation I can show if you like.
So, if you get right up in the astronaut's face, the visor will occupy most of your visual field. The virtual image of the sun will still be some distance away and occupy much less of your field. As you move away, the visor "gets smaller"(occupies less visual field) very quickly while the sun's image gets smaller at a slower rate because it was already farther away. The net result is that the sun's image will occupy a larger percentage of the visor as you move farther away.
I tried this out with the convex passenger side mirror on my van. At 1ft away, the sun occupied maybe 1% of the mirror. From 30ft away, it occupied about 50%. Alot of that 50% was probably glare and not actual sun, but thats probably the case with the photo in question. I bet if the photographer moved far enough away the glare would obscure the other guy's whole helmet.
Long story short, the sun reflection is bigger (proportionaly) because the guy is farther away. You would have to find another photo, taken from a similar distance and with similar lens filters to make a real comparison.
