Slice (at 0.5) a 5-Hi (120-cell) with a hyperplane direction cell-1st. Do the same to a 6-Ex (600-cell), same depth but direction vertex-1st this time. Save the two slices (polyhedra) for comparing.
The 1st is the dual polyhedron of the latter and vice-versa. I've not gotten the exact same scale but the solid angles are equal & the scale factor between the two figures (better, between one figure and the dual of the other) is about 1.085.
But, pay attention, 5-Hi-0.5-V1st is *not* the dual of 6-Ex-0.5-C1st...