Halliday & Matthiessen (2014: 364):
There is also some overlap between nominal groups and prepositional phrases. … the distinction between participants and circumstances is less clear in the ergative organisation of the clause, and this means that certain participants (Agent, Range, Beneficiary) are realised by prepositional phrases to indicate a special status in the clause as message (when they are presented as early or late news … ). At the same time, circumstances of location and extent may be realised by nominal groups without a preposition marking the circumstantial relation … .