With an zero output impedance amplifier having a infinite input impedance the amplifier must supply -29 gain minimum for oscillation to occur. Excessive gain increases harmonic distortion, but improves startup. The nominal input impedance of the network is about 2.6 times the shunt resistance in magnitude and quite capacitive.
The minimum phase shift network shunt resistance should be large with respect to the amplifier output impedance to reduce amplitude loss and pulling of the frequency, but also small with respect to its input impedance for the same reason. There is some lattitude here, as additional amplifier gain can compenstate for network loading. Non-infinite amplifier input impedances can be absorbed into the final network shunt resistance, but excessively low impedances require large gain to compensate for divider loss.