I'm not sure if the leak is really proportional to the surface area. (It's probably even less due to how the heat equation works). The equation for the thermal

I'm not sure if the leak is really proportional to the surface area. (It's probably even less due to how the heat equation works). The equation for the thermal resistance of a cylindrical system is explained in https://youtu.be/6x-jdCGWuHI?t=801 https://youtu.be/6x-jdCGWuHI?t=801 The thermal resistance is the sum of 3 (or more) terms, and while the outer terms are indeed proportional to surface area, I'm not sure if the physical constants of the system aren't designed so that the middle heat conductive terms of resistance R=ln(r2/r1)/(2pikL) is the dominant factor.