Those missiles are very, very large.
But not without precedent. These missiles are 6 meters long by 0.8 meters in diameter, which puts them in a similar class with many real-world anti-ship missiles (that's essentially what these are in an outer space context). These are probably a little bulkier on average, but they are required to operate in an airless environment where they must provide all of their own propulsion for both thrust and maneuvering, often over vast distances. Also, these are intended for use against much larger ships, so the warheads are probably bigger.
Though probably not as big as the crew would like.
Actually, it is probably a good thing that they aren't any bigger, since the bigger they are, the easier they are to hit.
What are they supposed to be, small thermonuclear warheads? I'm no engineer, but I'd imagine that if they get hit while in their silos, that wouldn't be a good thing. I'm almost a little surprised that they don't have any hatches to conceal them now that I think of it...