So we originally planned to use Top to Bottom (“Down”) instead of the current Up, but we ran into all kinds of issues with mis-detection. In our testing, it’s incredibly natural to slice at a sort-of 45 degree angle (making a “X” pattern) when doing left and right alternating strikes. And it’s even more common when you’re fighting something that’s low to the ground, like the Wererabbits, for example.
So basically by using Up instead, you can be pretty darn loose with your Left/Right swings, including swinging at 45 degree angles, swinging at things that are smaller than you, etc, and it still registers just fine as a Left/Right swing. Then we can also be pretty loose with the “Up” detection as well, because as you have pointed out, it’s very unlikely you would swing upwards unless you were intending to do it as a combo move.
So, I guess long story short is, in our actual testing we found that using Up was much more reliable for detecting the strokes for the combo moves, and it makes it very clear that it’s what you intended to do, whereas Down is something you end up working into your natural swinging motion way too easily/often for it to be a reliable indicator of a combo move.
I think this is one of those things where you’re just going to have to try it and see what it’s like when the test starts. It’s not that I wouldn’t change it, it’s just that I think based on actual testing it makes a lot more sense than it might seem on paper.
EDIT: To be clear, doing it this way allows us to, I think, match the looseness of the detection to the natural motion of your swings. You don’t by any means have to slice upwards vertically perfectly, really just about any mostly-upward motion should register as an upward strike.