  The aim of the article is to investigate the relative dispersion properties
of the Well Mixed class of Lagrangian Stochastic Models. Dimensional analysis
shows that given a model in the class, its properties depend solely on a
non-dimensional parameter, which measures the relative weight of
Lagrangian-to-Eulerian scales. This parameter is formulated in terms of
Kolmogorov constants, and model properties are then studied by modifying its
value in a range that contains the experimental variability. Large variations
are found for the quantity $g^*=2gC_0^{-1}$, where $g$ is the Richardson
constant, and for the duration of the $t^3$ regime. Asymptotic analysis of
model behaviour clarifies some inconsistencies in the literature and excludes
the Ornstein-Uhlenbeck process from being considered a reliable model for
relative dispersion.
