PFC related question regarding SQRT(6)
Ratio of peak to RMS for the sine is 1/\$\sqrt{2}\$. Ratio for triangle is 1/\$\sqrt{3}\$. I think the waveform you are dealing with is a triangle wave within a sine envelope, hence the product of the two factors.

https://www.fairchildsemi.com.cn/Assets/zSystem/documents/collateral/onlineSeminars/Understanding-Interleaved-Boundary-Conduction-Mode-PFC-Converters-WP.pdf  Fig 2 looks pertinent.