Best time to use EX fireball during traps ?

[Fatality XBL]

I usually use this when i got the frame traps going, at about the time when I do F+3, 3. So hypothetical frame trap situation here:

[On Block]
F+3 2, D+1, 2, F+3 3 xx EX fireball, continue trap...

So I'm just wondering, after what normal(s) should Johnny do EX fireball to get the best situation on block to keep the trap going.

 

[Name v.5.0]

I personally dont like the F+3,3 EX FB, it feels disjointed and doesnt always come out like I want it to. I then to do this: F+3 2, D+1, 2, 1, EX FB, 2, 1, EX FB, 2, 1, EX FB, F+3, 2......so on and so forth.

In all reality, I very rarely go the distance with the EX FB's. I feel like it's a total waste of meter. I only use it when I know the opponent's got less than 30% health because it will likely kill him.