Hi, JH, I'm sorry but I must admit that I simply don't know the answer to your question.
All I can say is that a Christian believes prayer to be a gift from God. And since Christianity is a communal fellowship of the many, as opposed to a restricted, even exclusive membership, it is as much a communal activity as it is a deeply private affair.
The Pauline epistles were written by a man who was deeply committed to prayer. He is constantly breaking out into thanksgiving, adoration, petition, and doxology, A good summary of Paul's teaching on prayer is found at 1Tim 2:1-8.
Christianity has often been described not, as a religion, but a relationship. Not just a relationship of the individual, but the wider community of believers at large to God. As Paul shows at vs 8 of the above mentioned text, the prayers of the many evidently are as effective, if not more so, than that of an individual. Why? Dunno. Paul did'nt elaborate. He merely recommended.