Jetta rear tires

I've purchased 2 sets of new tires in 3 1/2 years for my Jetta due to unusual wear patterns. The front has been aligned 3 times for various front end work, and the rear aligned about 2 months ago. The last set was put on 2 weeks ago. Assuming current alignments are correct I can smell burning rubber on the rear tires after I drive on the highway for a while. Looking at them from the back of the car they appear to tipping in about 3 degrees symmetrically at the top which would seem to account for the inside 1/3 wear I was getting before. With proper alignment and tire rotations should I expect this type of wear on the rear tires, and should they be leaning in at the top or should they be 100% vertical.