FourierShape x_cent and y_cent parameters do not make any difference about legume

[momchil-flex]

Unfortunately shapes cannot overlap in legume, this is briefly discussed here. In simple simulations, you can go around this by just discretizing your merged shape as a Poly - note that FourierShape is just a wrapper around Poly, using a finite number of vertices to discretize the continuous Fourier shape. So this is doable, just needs a little more effort from the user. The real problem is optimizations, in which case ensuring shapes do not cross may be trickier. Unfortunately this is a fundamental limitation of the fact that we compute FT-s analytically for each shape, rather than on e.g. a finite grid after taking shapes overlaps into account, etc.