The weight for donations in engagement segmentation does not count every individual donation in a sustaining gift series.  Instead, the segmentation counts the entire sustaining gift as a single gift.  

For example, if a constituent set up a sustaining gift to donate once a month and let it run for 12 months, then the weight would be 1, even though there were 12 donations.  Additionally, the segmentation only counts the first donation in the sustaining gift series. This means that if the sustaining gifts began before the timeframe that you specified in the task, the weight would be 0.