As the formulas suggest Geometric Brightness (GB) does not take into account magnification.
You can rework formulas above to correlate Twilight Performance (TP) and Geometric Brightness (GB):
TP=Magnification * SQRT(SQRT(GB))
Which basically says that the object may appear slightly less bright, but if it is more magnified to your eye you might see it a little better. However, higher magnification really diminishes field of view.
Anyhow, if you want to compare the performance of several scopes you should really compare them at the same magnification. At the same magnification, a scope with a larger objective lens will always have better twilight performance.
You have to first figure out what magnifications you want to use and work off of that.