Small angle neutron scattering (SANS) experiments are analyzed using a recently developed and properly generalized one-field effective free energy method. In the case of experiment of Keimer et al. on YBa 2 Cu 3 O 2 , we show that the fourfold symmetry of the underlying crystal is explicitly broken, but the reflection with respect to the  and  axes remains a symmetry. The vortex lattice also becomes generally oblique instead of rectangular body centered. An unexpectedly rich phase diagram is described.