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I usually can't help but to think in terms of dialectic. You can look at most spreads in dialectic terms, and the celtic cross seems to be the snuggest fit.
In fact, I'd say the first six positions , the actual cross, is a "double" dialectic, resulting in positons 2 and 5 respectively, either one fitting the role of thesis/antithesis its self. These in turn synthesize resulting in the more linear continuation of the spread.
I see positions 1,3,4,6 as simply being different "veiwpoints" on positions 2 and 5- resulting in some a priori insight (7 on up) into how the situation is most likely to unfold.
I'd be happy to explain in more detail if anyone is curious.