But you and FK keep avoiding the question: why do reformed pray?
Your prayers will change nothing since everything is predestined. Your prayers are not your prayers but robots doing what God tells them to do. Which makes prayers meaningless. Nothing that you do will change what was predestined. That includes praying (works).
We're not avoiding the question. You're not listening.
We pray so that we know if we're in the will of the Father. Paul prayed three times for his problem to be removed from him and God told him no. Paul prayer was answered and he knew what was God's will. David prayed to know what would happen if he stayed in town with Saul chasing him. God told him the people would turn him over. He got out of there.
God leads and guides His people by our prayer. If we fail to pray God leads and guides just as much but probably not in the way that is most comfortable for us to bring us back to Him. We know His will through prayer. Thus, we can pray that IF we are thrown into a fiery furnance, whatever happens, God's will will be done.