A capable editor does not come cheaply. 7% of earnings sounds like <$1 per 1k words during the guaranteed minimum period and effectively free during all other periods. Even if your novel is top 10, it won't be much more than $1 per chapter. Time is money, and that's seeking a dedication of half an hour - 2+ hours per day depending on how well you write and how much you want them to edit of a skilled trade which can otherwise pay from $5-25+ per hour.
Well, at least you are willing to offer something. Most who are searching for editors want free labor.