NBS, did you check the chart on the Fortress website?
FWIW, we bought our first Fortress to use as back-up, kedge, and stern if necessary (although we've never needed to use a stern anchor yet). Because of all those missions, I upsized one step from the Fortress chart.
Another reason I upsized is because of reading that some have found the Fortress anchors might "sail" a bit until you can get it down to the bottom. I've not ever experienced that, but if it were to be true, I'd guess it more likely to occur with their lightest versions. Just speculation, though...
We carry ours dismantled, in the Fortress storage bag. That's partly because it stows so well that way, and partly because the fluke angle selection is generally dependent on wherever the current location is, and the bottom type there.
South River, Chesapeake Bay