To shorten that particular task, simply remove items from the set-size <list> elements:
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Set Sizes for Letter Practice Phase
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<list PracLetterSetSize>
/ items = (2,2,3,3)
/ selectionmode = sequence
/ selectionrate = trial
</list>
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Set Sizes for Letter & Math Practice Phase
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<list PracBothSetSize>
/ items = (2,2,2)
/ selectionmode = sequence
/ selectionrate = trial
</list>
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Set Sizes for Letter & Math Test Phase
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<list TestBothSetSize>
/ items = (3,3,3,4,4,4,5,5,5,6,6,6,7,7,7)
</list>