Modeling growth minority capital investment

How can I model out a PF Income statement for a minority investment? No entry multiple or exit multiple. All I was given was that x amount will be injected into the company and that the injecting company would keep x% of increased revenue for certain segments.How would I calculate returns when I can only model to EBITDA? What I did was modeled out the amount of revenue that will go to the company based on the deal structure, applied the EBITDA margins for each year to get EBITDA and reduced this amount by taxes. I used EBITDA after taxes to get some type of cumulative return to calculate IRR but the numbers seem awfully low (~3-5% IRR) for a 10 year return. Can anyone point me in the right direction to figure out how to do this for my own learning? Maybe a site with a model? Couldn't find anything similar in the sites I been using for prep.