First scope inflation does not happen during the planning phase, it happens during the executing of the project, so we're not really talking about scope inflation here.
Reducing the scope is always in the hands of two people:
- The project sponsor
- The client
They need both to agree that the scope has to be reduced in order for you to be able to reduce it. But how can you get them both on board?
Well, you need to to do the following:
- Explain why reducing the scope will benefit the project as a whole and will accelerate its delivery.
- Explain that if the scope remains like this, then the risks will grow beyond proportions and there is a huge chance that the project will be over-budget and behind schedule.
- Convince the project sponsor and the client that some features can be easily transferred to a phase II of the project, where they will get a better attention.
- Ensure that only the features that the client want are included in the scope (do not suggest features yourself and do not allow your team members to suggest features themselves).
Finally, remember this: you have to make sure that the project will deliver an ROI, and a decent ROI, even after you reduce the scope. Put yourself in your sponsor's and your client's shoes, what's the point of finishing a project that doesn't deliver any ROI? So only eliminate features that the project can survive without.