Plate heat exchangers find wide application across various industrial sectors, and flow distribution within different plates significantly impacts their performance. Computational Fluid Dynamics (CFD) analyses conducted by researchers have revealed that flow distribution inside multiple channels of a plate heat exchanger is non-uniform and dependent on the inlet-outlet header configuration. In this study, we extended a reducedorder model to investigate flow rate and pressure drop within different channels of a plate-type heat exchanger featuring various header configurations. Our findings indicate that the flow behavior in uniform and tapered plate heat exchangers can be characterized by a common parameter (k). When k² is low, flow distribution tends to be uniform, with purely uniform flow achieved when k² is maintained at zero for uniform header. However, for the tapered header, the flow will be nearly uniform when k² is close to zero. Taper direction in the inlet-outlet header, plate structure, and quantity influence the magnitude of k², while its sign remains independent of the area ratio of the inlet and outlet tapered headers. Our analysis reveals that, for high values of k², excessively high flow rates occur in the initial channels, while lower or even negligible flow may occur in the subsequent ones. The results of this study have implications for the optimal design of heat exchanger header geometry to mitigate flow maldistribution in U-type and Z-type plate heat exchangers equipped with tapered headers.