  Lambda cold dark matter paradigm predicts that galaxy clusters follow an
universal mass density profile and fit a well defined mass-concentration
relation, with lensing clusters being preferentially triaxial haloes elongated
along the line of sight. Oddly, recent strong and weak lensing analyses of
clusters with a large Einstein radius suggested those haloes to be highly
over-concentrated. Here, we investigate what intrinsic shape and orientation an
halo should have to account for both theoretical predictions and observations.
We considered a sample of 10 strong lensing clusters. We first measured their
elongation assuming a given mass-concentration relation. Then, for each cluster
we found the intrinsic shape and orientation which are compatible with the
inferred elongation and the measured projected ellipticity. We distinguished
two groups. The first one (nearly one half) seems to be composed of outliers of
the mass-concentration relation, which they would fit only if they were
characterised by a filamentary structure extremely elongated along the line of
sight, that is not plausible considering standard scenarios of structure
formations. The second sample supports expectations of N-body simulations which
prefer mildly triaxial lensing clusters with a strong orientation bias.
