Took a pretty big gamble coming in from above and ending up just behind him in your pass. That dorsal is a 20mm gun, and it will handily take out a 163. I've made many a plane pay for allowing me a shot with the dorsal.
You would have been much better off coming in from below, like you did in that last pass. It's a good feeling when you nab two in one like that, I might add.
If you were against just about every other bomber, coming in high will be solid. But against a Ki, you really need to avoid giving him any kind of shot with that 20.