Would ground settlement occur ahead or behind the jacking face for pipe-jacking?

It is reported by Lake (1992) that settlements are expected at the ground surface at a distance of 1-2 times of tunnel depth ahead of the tunnel face and 80% to 90% of settlement to be completed at a similar distance behind the face. However, in the paper “Monitoring of ground response associated with pipe jacking works – recent experience in Hong Kong”, the author pointed out 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 tunneling face.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.