A noticeable magnetic field dependence of the vortex lattice distortio
ns in hexagonal unconventional superconductors is obtained below the s
econd order phase transition line H(T) (H*(T) < H(c2)(T)) for H perpe
ndicular to the hexagonal axis c. A range of the Ginzburg-Landau coeff
icients is shown where our theoretical results are in qualitative agre
ement with the neutron diffraction measurements in UPt3.