bobstay sizing

[osteoderm]

From The Apprentice I get the general procedure to estimate bobstay loads, but there's also the mention of an additional safety factor given the bobstay's vunerable (both to corrosion and impact) location.
Is the 2.5x (or thereabouts) safety factor supposed to be above and beyond the calculated load on the bobstay, or instead above and beyond the sizing of the jibstay (with its own inherant safety factor)? Going with the latter makes for a 14mm bobstay on my 32' cutter; seems a little excessive, but then again...
My dual boomkin shrouds have a healthier staying angle, but I'll make them the same size as the bobstay for more straightforward stocking of spare bits.