FF,
I don't think it's quite that simple. As I understand it, the best glide angle occurs at a fixed angle of attack which is constant whatever the weight.
This is covered in the manuals by a table which gives descent speeds for different weights.
In your case the speed is constant but the weight changes. In order that Lift=Weight, the aoa has to change.
So it all depends on how close to optimum you were when you increased the weight. If you were at the optimum aoa, then any change in weight, up or down, will result in a steeper descent because it will move the aoa away from the optimum angle.
If you're light and the speed for the best descent is lower than your actual speed, increasing the weight would result in a steeper glide angle because you will increase the aoa from the optimum.
If, on the other hand, you are heavy and the speed for the best descent is higher than your current speed, increasing the weight will increase the aoa towards the optimum which will improve the glide angle.