Welcome and congrats on the order Deepak!
As far as the QS8s, I would say about 1 1/2 to 2 feet above the listening ear position is ideal. But the QS8s are also very flexible and many report great results with them mounted even higher.
As far as the differing distances/heights- this may be more critical, but it really depends on how big a difference you are talking about relative to your seating position. They are forgiving so a slight variation may not be a problem, but you do want sounds panning around you to sound uniform as they were meant to. Can you share some room dimensions and seating/speaker locations or a diagram? That will allow us to help you more. At least you have the stands to fall back on if needed.
