GokyoShumyoSection3Problem79/Attempts

So why is this Ko and not clean-life like in the similar problem Gokyo Shumyo, Section 1, Problem 74?

It seems it depends on the strength of the black outside.

Seems to be Ko  

Reference: If white tries the same approach like problem 1-74, then black can make life in the corner and the position is still Ko.  

What about this ?  

Here W has the forcing move of killing black in the corner