Another way to look at the same problem
Best glide speed, (max distance for min hieght, not to be confused with min ROD, which will normally be min clean) is a function of wieght, that is why gliders carry water ballast. They can go faster for the same hieght lost against distance.
Now, given the aircraft descend at the same speed ( assuming it is above best L/D) then the heavy aircraft is in fact closer to its (higher) best glide speed, so is more efficient.
If you change the descent speed, to say best L/D the lighter A/C will always win.
In the triple 7, ( esp the 300 or er) a heavy A/C can be a bi***h to get down if you get slowed down, 250 is close to best L/D and you need boards to keep any sort of profile.