HMAS Sydney and the danger of closing a raider

Why did HMAS Sydney close so closely with Kormoran?

Sydney may have been trying to capture the suspected raider, but the decision gave Kormoran the opening to fire first.

One interpretation is that Sydney tried to close sufficiently to capture the disguised raider rather than simply destroy it at range. That required delaying fire while identity and intentions were tested. Kormoran opening fire first turned the calculated risk into a disaster for the Australian cruiser. The raider was also lost, but Sydney might have survived had she fired first from a safer position.