Maybe 1/4 of DR? The thing is, DR is actually quite large but Pica's golem is really insignificant in comparison to DR as a whole. This is part of Pica's golem inbetween the city's rubbles:
So DR is far far far larger than Pica's golem. I think there are also some calcs which calced Pica at 1 - 2km (still quite large) and DR being 40km in diameter. That's what I recall at least.