Accuracy of Lidar remote sensors for wind energy has been previously reported. Coherent Doppler lidars have shown very high correlation with calibrated cup anemometers in flat terrain, both onshore and offshore. However, in more complex terrain, not only more turbulent air flow but also loss of flow homogeneity happen, and remote sensors measurement process need to be closely examined. We compare and simulate cup¿s point and lidar¿s volume measurements to understand and explain for the two sensor¿s response. We put in evidence the main error term in the horizontal and vertical wind speed retrieval. Geometrical optimizations of the WINDCUBETM measurement process are also investigated to get more reliable wind speed estimate. We show our conclusions and the results of the CFD simulation performed on a Spanish complex terrain case.@en