That looks like a Santoku shaped blade, fairly straight. Some of them and most chef's knives are slightly curved.
What I was thinking of was curving the bottom of the "dish" to match the shape of the blade or slightly flatter.
The one I have now is very similar to yours with the onions, but not as deep.
I have made number rectangular ones that I dished out the center about a 1/4" and left the four corners the original height. There was about an 1/8" arch from corner to corner. this not only help to keep the juices from running of, but broke the suction with the counter top if they did.