> and that isn't the same as what can be done in a small-diameter missile

Which was the genius idea behind Track-via-Missile in the Patriot SAM

Instead of having the missile work-out the best interception based on what it can detect, it relays its view of the World back to the ground station which returns its recommended geometry. Constantly and at high frequency.

And since the ground station is more powerful and can be upgraded more easily than the missile's electronics, Patriot has made huge improvements since the 1991 Scud incidents.

In an anti-stealth context having each missile 'see' from a different angle and being able to fuse that I to one picture is also useful in defeating shaped reflections. It's like a network of remote, lethal sensors.