That's a good question and the issue seems to come up on the Euro Chair.
In shopping for a recliner for my elderly father, who of course came along to ensure it'd be comfortable, I was amazed at how subtle differences in seatbottom length, height, and firmness affected how one sat or slumped relative to seatback design, including lumbar support, all of which affect each of us differently based upon our build. And, what's good upright may not work reclined for everyone, followed by changes as the seating (and the one doing the sitting) ages.
I bet if PC respondees discretely describe their builds vs. comfort on particular seating like the split reclining sofa, we might all see some correlations along with whether some need to add pillows or something, also.