Shoulder position and back alignment have alot to do with your angles. A forward stance is easier on the knees if you like squaring off your shoulders, down mountain. Duck stances are good if your shoulders, back, and hip are more aligned- more "standing sideways" than down mountain- (not to referrence the walmart of snowboarding). This mostly affects your back knee as long as your front is set to +9 or more-
Even with a forward stance, you can still ride switch- especially if you shift more weight to the back foot, but its not ideal for switch.
I changed from duck to a forward stance this past season and its easier on my back knee- seems to work ok on the rails and boxes I hit, but I don't go into features switch at this point.
People hate to do this- but you need to take the time and try as many angles as possible to figure out what works. Take a day and just change your angles around every other run or so- its worth it in the long run.