I don't know about sizes but materials matter as well. When I set up any sort of lashing, I consider the strength of the twine, which is usually not all that reliably reported in any standard manner - safe working load, breaking strength, or whatever. So I figure useful working load about half whatever is on the lable and I take off another 40% for putting the line through a 180 degree bend. So each run of the lashing is worth about a third of the rated strength of the line. Then I add more as feels right.
It will be interesting to me if responsible and properly trained riggers agree with this rule of thumb. It's not failed me but that does not mean the engineering assumptions are correct.
G'luck
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