Correct formula for primary inductance
\$K_R\$ is the ratio of the peak to peak current to the peak current: -



So, for the flyback transformer above with 1:1 turns ratio and ignoring the fact that primary currents and secondary currents always fall to zero when the control voltage changes, the peak to peak current is 1.062 amps - 0.531 amps = 0.531 amps. Therefore \$K_R\$ is clearly 50%.

For DCM peak to peak current is the same as peak current hence \$K_R\$ is 1 across the range of loads it is used for: -



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