Remember my post about some bottle have more carbonation then others . Some of you guys suggest to rack the beer on top of the sugar solution, this way I will get better stirring and uniformity. I just figure out why I prefer to do it upside down, if you rack the beer first, you get to know exactly the volume of beer you have (fermenter minus yeast cake) and how much sugar you really need for the given volume and style.
You make a good point. Your way of doing it should be fine, as long as you stir (gently) in order to uniformly disperse the sugar solution.