In general in the soliton propagation the dispersion length and the soliton length are comparable to the fiber length. that means both dispersion and nonlinearity are included in the calculations.
if dispersive length is little longer or shorter than nonlinear length is no matter. the main concept is that the dispersion would be ignored or the nonlinearity will be ignored if their effective length is too longer than the length of propagation!!
Hope that clears,
thanks
Mohamed Abouseif