anchor: Regardless of where the SCR reactor is located, ductwork from the economizer outlet to the SCR reactor and back to the air preheater inlet must be accommodated.
positive: Ductwork from the economizer outlet to the SCR reactor and back to the air preheater inlet must be accommodated, it doesn't matter where the SCR reactor is.
negative: The ductwork from the economizer outlet to the SCR reactor and back doesn't need to be accommodated.