It's a molar ratio. In a perfect world, you need the same number of atoms as opposed to mass.

Neutron flux from fission reactors is on the order of 10^19 to 10^25 neutrons/cm^2/s depending on location in the core and would light be similar for fusion reactors. So you're correct you'd need the same amount of source material to generate 1 ton of tritium from 2 tons of Li-6 with 100% efficiency. However, you'd lose tritium via decay and hydrogen diffusion along with uncaptured neutrons paint through the Li-6 target.