"any more thoughts on the over-representation, or explanations for it?"

The Dando report gave a clear reason.

This has been posted more than once.

The reason is because these events occurred within a limited specific area.

The new Ceop report will be studying similar data to the dando report on a national level.

The dando report rejects the idea that street grooming is a crime.

This is because it is nonsensical to see it as a crime in its own right.