We present a theoretical calculation of the dependence of reflectivity Rpp of the improved fully leaky waveguide geometry, which comprises pyramid, matching fluid, and strongly anchored hybrid-aligned nematic liquid crystal (NLC) cell on the internal angle. The calculation is based on the multi-layer optical theory and the elastic theory of liquid crystals. For different sums of flexoelectric coefficients e11 and e33, the curve of Rpp moves a distance to the left or the right relative to the case of ignoring the flexoelectric effect and the distance of the movement varies with different flexoelectric coefficients. Consequently, the sum of flexoelectric coefficients can be explored by measuring the distance of the movement.