I would think that since the absent student did not complete an evaluation for the other students, then zero points would be added to each of their scores in lieu of an assigned score by that student.  If you divide a students' received total points by 6 (rather than 5), then you would eliminate the escalation of the students' scores. 
Say a student received 121, 119, 122, 119, 118 from her team mates. Then by adding zero for the absence of a score from the absent student, and dividing by 6 instead of 5, this student would receive approximately 99% of the available team points.
Hope this helps.

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