 Thermoelectric couple figure of merit

For a constant-property pair with Seebeck difference ${\alpha }_{np}$, electrical resistance $R$ and thermal conductance $K$, $Z_{\mathrm{pair}}={\alpha }_{np}^2/(RK)$. With identical legs of individual resistivity $\rho$ and thermal conductivity $\kappa$, this is ${\alpha }_{np}^2/(4\rho \kappa )$, not ${\alpha }_{np}^2/(\rho \kappa )$.