In NFPA-13, section 126.96.36.199
Our local code official states that we need to separate stacks by 8 ft AND have 25 ft of separate between commodities.
Our understanding is that it's either-or. Either we have 8 ft separation between stacks OR the stacks are separated by 25 ft of commodity.
Our layout does not allow for both: both 8 ft of separation and 25 ft clear of commodity.