Post-hoc priors

[mcfanda]

Hi,
it seems that in post-hoc, the prior probabilities of the comparisons are computed using pH0^(2/k), where k is the number of levels of the factor. However, in Westfall, Johnson and Utts, 1997, the suggested adjustment is pH0^(1/k). What is the idea behind using pH0^(2/k)?
thanks