We made it work by adding a dowel.
This wasn't quite what I expected. I'd anticipated that "Separate Seat" meant there was a encasement for the seat cushions that was separate from the main slipcover. There isn't; instead there is extra material that slips under the cushions and then two seams that delineate the front of the seat cushion(s) to make it look separate. So far so good, but my loveseat also has separate back cushions which made it tricky. We got the seat covered and in place and then added the back cushions. There was not enough material in the rest of the slipcover to cover the back cushions, to tuck in between the seat and back cushions, and then to cover back of the loveseat. If the seat cushion coverage had been separate as I'd envisioned, it all would have been just fine. In order to make this work, we had to shove a dowel (broomstick) between the seat and back cushions and basically left most of the back of the loveseat uncovered. The dowel doesn't really "want" to go there so it is a bit visible in a couple of places. Beyond this, I really like the color, the material and how it stretches. The material itself is actually much nicer than I'd anticipated and I like the looks of the final results.
Bottom line: Think twice if you have separate back cushions.