Equity waterfall logic

One of the CRE dev projects is split into two mini projects. They have two separate loans, construction timelines, being sold at different dates, etc. but combined act as one big project. There is currently two equity waterfalls, one for each phase. Once they’ve beeen calculated, the contributions/distributions are combined for the project level totals. I’m currently trying to consolidate by using the combined cash flow of the two phases to calculate the returns, but am a few million off than if doing it separately then combining. Is there a good argument for keeping the waterfalls separate, then combining the returns vs. combining at the cash flow level and calculating returns off that total cash flow? Like is one more “accurate” or is it a matter of preference.