Symmetric PIR capacity conjecture for MDS-coded colluding and adversarial servers

Assume $n>k+t+2b+r-1$, where $t$, $b$, and $r$ are the numbers of colluding, Byzantine, and nonresponsive servers, respectively. Consider symmetric private information retrieval (SPIR) from an $(n,k)$ MDS storage code with $t$-collusion, $b$ Byzantine servers, and $r$ nonresponsive servers.

Symmetric PIR capacity conjecture. The capacity of SPIR is

$$1-\frac{k+t+2b+r-1}{n}.$$

The conjecture is one of the claims for the known-parameter cases $k=1$ or $t=1$, where symmetric capacity is observed to coincide with asymptotic nonsymmetric capacity. The source notes that an earlier formulation used denominator $n-r$ because nonresponsive servers were excluded from the download cost; the paper counts them, while stating that the results apply under both conventions. Its resolution is not established in the supplied text.