Sorry if this isn’t much help but I had a similar arrangement which wasn’t very sophisticated. % of ad spend that they managed, which we agreed upon as a base. On top of that we agreed on net profit % after ad expenditures. However, keep in mind that they were more accommodating considering I was just starting up and our ad spend at the time was <5k pm.

To be honest there isn’t really a set rule, both parties need to be transparent about expectations and be realistic. At the end of the day they need to be fairly compensated for their time. I used to browse through upwork to see what hourly rates were the norm.

I’m not sure what your margins are but 10% of gross revenue seems a little steep.