Plantwide regulatory control system design for a monoisopropylamine (MIPA) process is presented from the perspective of plantwide transient variability propagation. The process consists of a hot reaction section followed by a cold separation section with three columns and a decanter with two liquid recycles. Two control structures with the throughput manipulator (TPM) at, respectively, the limiting reactant fresh feed (CS1) and the decanter feed (CS2) are evaluated. The decanter level control scheme dramatically affects the overall plantwide response speed. The response is extremely sluggish when total decanter hold-up is regulated using the organic outflow (Scheme 1) and is significantly speeded-up (> 3 times) when the total (organic + aqueous) outflow (Scheme 2) is manipulated instead. The reason is traced to Scheme 2 effectively propagating water imbalance transients out of the plant to the water by-product stream and not to the organic recycle stream, which disturbs the side-product recycle-to-extinction balance. The case-study affirms the heuristic of structuring the plantwide control system to propagate transients out of a recycle loop for improved dynamic performance.