The only thing I keep finding is:
(a) A petition for modification or termination of an existing support order shall specifically aver the material and substantial change in circumstances upon which the petition is based. A new guideline amount resulting from new or revised support guidelines may constitute a material and substantial change in circumstances. The existence of additional income, income sources or assets identified through automated methods or otherwise may also constitute a material and substantial change in circumstances.
You'd figure they would specify a percentage or something. One person may view 5% as substantial and another person may only view 10% and above as substantial.