Comparison between the theoretical and observed turbulent quantities as a function of heliocentric distance. Top left and right panels: energy in forward and backward propagating modes. Bottom left and right: normalized residual energy and the normalized cross-helicity. The solid curve denotes the quasi-2D component, and the dashed curve represents the slab component. The red and blue squares are the observed quantities measured by PSP and Helios 2 with error bars, respectively.