yup on my airplane as well: less weight means steeper descent
simplified:
the composant of weight acting towards your flight path is added to your thrust (weight*sin angle)
if you take 2 planes at same angle of descent but different weight:
aircraft heavier will need more drag or will accelerate until drag=thrust
if both descending at idle and speed limiting (as Vmo) then the heavier aircraft will have to reduce its descent angle compared to the lighter one
Correct me if I'm wrong, thanks