Ground settlement occurs ahead or behind the jacking face for pipe-jacking?

It's reported by Lake (1992) that settlements are expected at ground surface at a distance of 1-2 times of tunnel depth ahead of tunnel face and 80% to 90% of settlement to be finished at a similar distance behind the face. Though in the paper 'Monitoring of ground response associated with pipe jacking works - recent experience in Hong Kong', the author highlighted that based on their experience, development of longitudinal settlement was observed at a distance of 3-4 times of tunnel depth behind the tunnel face and little settlements were reported immediately above the tunnelling face.