A basic sailcloth principle:
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Tension along one edge loosens opposite edges by dragging cloth away from them towards the source of the tension.  Excessive cunningham will, for example, produce floppy leeches, and a lowered spinnaker pole, which is like applying cunningham by stretching the spi luff,  will loosen the leech of the spi also.  If you loosen the outhaul, you firm up the leech, and so on.
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