This work shows that the tortuosity assumption in NODDI can not be identified as the source of incompatibility when the model is extended to data acquired with tensor-valued diffusion encoding. NODDI, originally developed for multi-shell linear tensor encoded (LTE) data, was shown to be inadequate when extended to LTE and spherical tensor encoded (STE) data jointly. The adoption of tortuosity assumption by NODDI has been suggested as a plausible explanation. We conduct a systematic model-comparison study to show that this explanation is inaccurate. We identify a different assumption of the model, the equal-axial-diffusivity, as a source of incompatibility.