In an Outsourcing IT project we are are trying to estimate the relationship between the governance cost and the project size in FTE.
For example, if the governance cost of a 500 FTEs project is X the cost for a 1000 FTEs project won't be 2X. It will grow up but not in the same proportion.
Is there any benchmark or guidelines that describes this relationship?
I don't think so as it depends on the composition of your FTEs. If you have 500FTEs of developers, you may need different governance than 500FTEs composed of 300FTEs of developers, 200FTEs of Testers and 100FTEs of Business Analysts and Architects.
Also, you should also acknowledge that the level of governance may vary based on the phase of your project.
I never saw any formula or guideline, but talking about parametric estimation, you should define your parameters based on your FTE composition and apply some sort of sanity check to assess if the level of governance is appropriate to your project.
Good practice is to document these parameters and refine it over the time based on lessons learned from previous projects
