When to shield bunker in a blockstring

[Braver]

How do you know where in a block string to shield bunker?
Every time I'm blocking and I try it, I usually always fail.

[Tempered]

as Hmoon anytime the opponent does something other than an A attack.

For C and F during multihit moves is generally best. Some exaples would be Hvsion 5c or Len 5b