An example:
$C_1=[(0,0),1]\;,C_2=[(1,0),\frac{4}{5}]\;,C_3=[(2,\frac{3}{2}),\frac{3}{4}]\;.$

Contours show equal distance sums.
$d_{\min}=\frac{3}{4}$ is achieved at $p_{\min} \approx (1.06, 0.80)$.
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  [1]: https://i.sstatic.net/bxPNf.jpg