I've been flying an 11m Ozone Edge with non-stock lines, all four the same diameter. (Stock Ozone Edge rear lines are considerably thinner than the fronts.)
My kite has a possible tendency to stall when the lines are heavily loaded. I wonder if this is because the kite is tuned by Ozone to maintain reasonable trim under load with relatively stretchy rear lines to compensate for the greater loading and therefore stretching of the front lines. In my case, the front lines obviously stretch more than the rears under load, relative to the stock line arrangement, but I don't know to what degree.