Permafrost is right.
Best L/D ratio is a property of the airfoil, just that. Weight does not influence the best L/D ratio; you'll just find at a different speed.
Provided you fly at best L/D ratio speed (green dot when OEI) your descent gradient is the same at all weights.
However:
In normal ops (flying let's say 290 kt for descent) we will have a worse L/D ratio at low weight (so a worse gradient) because we have a larger margin to green-dot/best 'L/D' ratio than with a higher weight. Hence the common misconception that a lighter aircraft will descend more rapidly than a heavier one; this is only the case when flying fixed speeds for descent (or a ECON speed for that matter).