Drobo S - capacity vs. actual space

Hi. I am trying to assess my potential storage capacity using a Drobo S 2nd gen. If I use 5 5 tb drives (I know the drive capacity is theoretically 4 tb but I know 5 tb drives work in my Drobo second generation so I suspect they will work in the Drobo S as well) that gives me 25 tb of theoretical capacity. I also know the max volume size is 16 tb. If I enable dual redundancy does that get substracted from the 25 tb, leaving me somewhere in the range of 15 tb of actual capacity (under the 16 tb limit) or does it get subtracted from the 16 tb leaving me with around 6 tb of actual capacity. I’m assuming it is the former but can’t find an answer online and the calculator doesn’t work for the Drobo S any more. Thanks for any advice.