The Cross|Up can spread the work to both hands with KBDs to make them easy and efficient:
Hold Back with the stick
Then tap Down on the D-Pad (right hand)
Then tap Forward on the D-Pad (right hand).
Repeat [tap Down / tap Back]
Be sure to separate the Down and Forward inputs by tapping very crisp and precise. If you accidentally tap Down + Forward on the D-pad, you won't get a Back Dash at all! It is not a quarter circle motion, it's a "Tap-Tap."
Also, be sure to let you Back Dash finish before inputting another one! As soon as you tap Down again it will cancel the dash. Every character has a nice sweet spot timing to get the best KBD.
In case you're wondering how the hell this is actually is getting you a KBD:
Left + Right cancel each other out to Neutral, even if it is Analog Stick Back + D-pad Forward!
So our literal inputs are Back [Down-Back, Back, Neutral, Forward]. When we tap Down, it cancels our Dash into crouch, then when we release the button it returns the stick to "Back." Then when we tap Forward, we get SOCD Neutral (Left + Right), and it returns the input from Neutral to Back as soon as we release, giving us our Back Dash!
Just a little ergonomic input science for ya'!