We got a review on this credit that we don't know how to address...

We are working on a multiple building Project and there is an area within the site designated for future expansion of this industrial plant. The review comment ask us to ensure that "future development is included in the calculations". A few things:
1) As of today the owner only has an estimative of the area that will be developed. So how can we calculate a percentage of a number we doesn't have?
2) Would a letter from the owner commiting to comply with this credit in the future expansion area be enough to justify the review comments?

Thanks