"However, the position of the window with regards to the wavelengths absorbed or transmitted, and the width of the window, is due to the inherent properties of each of the gases and not the quantities"
This is correct.
The graphs we are talking only show the relative distribution of amount of energy absorbed relative to the wavelength.
However the total amount energy absorbed and radiated back to Earth is proportional to the quantity of the green house gas. Of course, the quantity is not shown on the graph.
