Polarimetry extends the dimensionality of SAR data (to 3 or 4), so the necessity to have multivariate statistic (and non-Gaussian, because of the high resolution) distributions as models for PolSAR data: such are the SIRV (Spherically Invariant Random Vectors). However, as the statistic model becomes so complicated, correctly estimating its parameters gets difficult. More, although they are versatile, the SIRV models are not guaranteed to match the PolSAR data. To evaluate the pertinence of those models with respect to the PolSAR data, through one of their most important statistic property, namely the circularity, it is the purpose of this paper.