If a knife is ground 70/30 (as an example only), the edge should be ground 70/30. Doesn't matter if it's convexed or flat. The center line of the knife grind needs to line up with the center line of the edge. When it's not, it can affect performance.
All that said, in most knives ground 60/40 or 70/30 having the edge off axis a little bit doesn't affect the performance at all. It's when someone takes a 60/40 knife and grinds the bevel 90/10.....or a 90/10 knife and grinds it 50/50....that issues start showing in cutting ability. At the end of the day, if you're very in tune with the performance of your knife, you'll notice changes easier than most people. Race car drivers notice the slightest changes in their high performance cars.......most drivers don't know when a wheel has fallen off.