An alternate view, page-24

SPO could also issue a small profit warning , which would give grounds for downer calling it off, although they wouldn't necessarily do so.

SPO has advised shareholders to take no action. Many holders bought well above the offer price and may see the offer as opportunistic and would rather try their luck by holding rather than taking a loss. They could struggle to get 90% acceptances.
After all the flack Downer has copped, they certainly won't be increasing their offer and are more likely to use any opportunity to walk away, at which point share price should be re-rated.