The sub-threshold region variability due to TiN metal grain work-function induced fluctuations in a 10.4 nm gate length In0.53Ga0.47As FinFET is analysed for three different cross-section shapes (rectangular, triangular and bullet-like), using an in-house 3D Finite-Element Density-Gradient Quantum-Corrected Drift-Diffusion device simulation tool. The Id-Vg characteristics in the sub-threshold region have been compared for the three cross-section shapes. The device with more triangular cross-section results in lower off-current, drain-induced-barrier-lowering (DIBL) and sub-threshold slope values. However, the cross-section shape has a very small influence on a metal grain work-function induced variability in the threshold voltage with differences of only 4% between the different device shapes. We also present a new approach, based on the creation of Gate Sensitivity Region Maps, to evaluate the sensitivity of the different regions of a semiconductor device to the metal grain work-function induced variability.