Note, too, Footnote 3 in B31.3 - "A single intensification factor equal to 0.9/h^(2/3) may be used for but ii and io if desired." This applies to the entire table.
I can't say it is more than gossip but I heard it said that the B31.1 people didn't think engineers could easily identify in- and out-plane orientation, therefore, no ii & io there.
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Dave Diehl