Well, I don't think it is neccessary to complicate your mod any farther. Extra flag for high-level cargo would be nice but not that important. It is just pitty that right now AI will _never_ever_ use cargo bays II and III, it is a completely lost tech for it.
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Unrelated issue: I think it is a typo in standard (and every other SE IV mod ! ) systemtypes.txt file, but tri-star system II, one that is without any planets, should have a flag "empires can start in " false instead of true. Otherwise it is quite odd to have a homeworld in supposedly planet-free system. It happened to me just right now
