In regards to 6D j.D fuzzy guard set ups... they are pretty strange. I spent some time testing this out, and it had some really strange results. Tests were done on Jin in both regular block and IB, midscreen. Barrier block was not used cus lol pushback.
Instant Blocking the 6D j.D resulted in: j.A and j.C would hit but Ragna would cross over Jin, causing his j.D to whiff. Should work 100% in the corner, although I did not test it fully.
Regular block resulted in: oddly enough, the entire j.A j.C j.D string would hit, although the timing on the landing the j.A fuzzy seemed a bit weird. It seems like you need to the 6D as close as possible (momentum might help) in order to land the full combo.
j.A 623D(1) RC should work on IB and regular block, but that was something he could do for a while now.