Being able to change the atmosphere height without changing its mass wouldn't be accurate, considering it is not possible in real life. The quantity of air and the gravity of the object is what determines the height. Also, the Earth wouldn't even be able to hold the atmosphere at a large distance, such as the distance to the Moon anyway. However, I do agree that by changing the mass of the atmosphere, it should get have a greater altitude, with the limit being where the gravity of the object is no longer able to hold any more air.
On the other hand, if you increase the mass of the atmosphere, the pressure will be greater in the bottom, making it more compact... and the height wouldn't change in a linear way. Then some calculus would be necessary, which would make things too complicated to be implemented