The percentage that is overhead will vary, but only by so much. Otherwise, someone will come along and find a way to undercut your prices and take your business. It's reasonable to assume that if one hourly cost is double another, the developer's pay is higher.
(Not denying someone might find a way to really pull a scam in the short-term, and find a kid they can pay minimum wage to, but that's not a scalable or stable arrangement).