I'm 193cm 104kg (6'4'' 230lb) and have some issues with patella tendon. I have the ergo +20mm seat. It helps a little, but it's more about comfort of the butt than legs. The biggest help is sitting further back. Doesn't cost anything so try it.
I tried lowered footpegs (the cheap ones, not the full rear set), but that messes the angle of feet to change gears which adds to muscle tension. Also, KTM tends to have different seating triangle than most bikes, almost motard style - footpegs are lower and almost exactly under the seat, so if lowered even more it makes them more easy to catch on things when leaning the bike. Luckily never happened while riding but definitely when maneuvering the bike into the shed. You may have a different experience, but for me it was annoying.
Adding an extra cushion, eg airhawk, seems to work a lot better. The downside is then you lean forward more, and it was not comfortable for my back and wrists - handlebar risers and adjusting angle of levers fixed that. Overall I would say cushion and risers is way to go, especially if you can set it up so it encourages you to sit further back rather than slipping onto the fuel tank.