The investors are very unlikely to make 71%. They might make 300%, 20,000%, 80%, 30%, 0%. It's very unusual for a business to make exactly the income shown in the business, incur the same costs shown in the business plan, or achieve exactly the profits shown in the business plan.
You mention a 71% profit on investment - that only occurs in your projections. Once the business starts, the projections go out of the window, and real-life results occur.
You have to balance risk and reward.
There are no hard and fast rules for this. You just have to come up with something that both the company and the investors are happy with.