The theory that describes the arising twist-bend periodic walls at the neighborhoods of the Freedericksz critical point affirms that the mode with the fastest initial grown will fix the observed properties of these patterns. From this principle it follows that just above the Freedericksz threshold there is a region where this leading mode becomes null and, therefore, a homogeneous bending of the director would be detected. This prediction was not confirmed by the experiment and walls with very well defined wavelength were found. We will shown here that around the Freedericksz threshold the fastest growing mode can not be defined and a new way to compute the observed structures will be proposed.