We are building software for a medium-sized company 'X'. Software is unique but strongly depends on data which the company 'X' can gather and plug into the software.
We develop that exclusively for them and for fix-priced milestones. We've learned that company 'X' has intention to sell this software in more countries.
Company 'X' is willing to make a service contract with us but only for 20% of cumulative price per year (which is OK but pretty low compared to their potential revenue).
Are there any standard models for this scenario? Can we ask for some extra money for each country?