If we're talking pure glide then then there is no thrust. For a given aircraft configuration, the best glide range will occur at a fixed angle of attack at which the L/D ratio is a maximum. At this fixed aoa, the lift coefficient is constant. The extra lift force required for the heavier weight is supplied by the increased dynamic pressure and not by an increase in AOA. I'm not sure this really answers the original post , which concerned itself with constant speed descents. At constant aoa, the glide dynamic pressure is constant, however the glide velocity will decrease as the air density increases at lower altitudes during the glide. To maintain constant velocity during the descent, the aoa must be varied such that the required dynamic pressure increases in proportion to the increase in density during the glide. This will produce a constant speed glide. Note that the glide range will no longer be the best glide range for the aircraft and that the flight path angle will be steepening during the glide.