No worries bro, there's no rush.
Like, as far as I've seen from my fights, cross-up j.C works depending on a few factors:
-How high you are in the air
-How tall your opponent's character's is
-How wide your opponent's character's hitbox is
For example, I've done it low to the ground against Bang before, but when I went into training mode, I found I couldn't do the same to Jin or Ragna.
When done from higher up, it can be made to work on skinnier characters such as Jin or Ragna, but that also makes it harder to capitalize off of, since j.D does not have a cross-up hitbox, and so you might have to rely on D or C ID and a rapid cancel.
Not sure how useful this will all turn out to be, but I absolutely love cross-ups, and you wouldn't believe how ambigious this can look.