Alex,
If you are refering to the CAP 698 then I suspect that it is a bit more complicated than simply reducing weight and increasing V1 as contamination depth increases.
The main tables on pages 72 and 73 certainly show both TOM and V1 decreasing as mass increases.
But the VMCG Limited Mass tables show that the mass increases as contamination depth increases. At 6600 ft field length and 4000 ft PAlt for example the figures are 45K at 2 mm depth, 48K at 6mm and 52K ar 13 mm depth.