Partial capacitances of a system of conductors - conductor acting as a shield

I have a small question about the following problem. The figure represents the cross-section of a three-conductor system comprising a communications coaxial cable of length l running parallel to a conducting wall (reference conductor). Determine the partial capacitance scheme of the conductor system.

So, I had zero troubles finding out the capacitance between conductor 2 and zero and between conductor 1 and 2.

$$C_{20} = \frac{2 \pi \epsilon_0 l}{\ln (\frac{d}{r_2} + \sqrt{(\frac{d}{r_2})^2 -1})}$$

$$C_{12} = \frac{2 \pi \epsilon l}{\ln (\frac{r_2}{r_1})}$$

However I'm having trouble understanding why $$C_{10} = 0$$. My guess is that somehow conductor 2 acts as an electric shield between conductor 1 and conductor zero, so that the electric field due to conductor 1 is not "felt" by conductor zero. However I'm not sure if this is correct and would like some more insight about this. Can someone help me?