What is the value of the the product inventors contribution?

I'd really appreciate your feedback/opinion on this scenario as it affects some rules I writing for a new platform. An inventor has taken a year off paid work; performed multiple experiments building different products, finally iterating to a working MVP that shows promise. The inventor now needs co-founder(s) to bring the product to market. "On-paper" what is the **value** of the inventors contribution to this point? I'm looking for your instant 'gut' response on what is fair: Note: 5x and 10x denote risk ratios. That is the risk they've taken that their effort would not receive a return.