I came across this with CSZ today.
I know J1 is +15 on hit and J2 is +24 and I was trying to use the advantage to set up a 50/50 but I got a knock down instead of a launch on the overhead B2.
This only happens after being airborne. This doesn't happen with a regular standing B1 2+4.
Only a deep J2 links to B2 so technically J1 should work every time.