I might be wrong but to me Shield Matrix level 2 heals less HP than Shield Matrix level 3, however Shield Matrix level 3 has an explosive attack at the end.

The problem comes after the explosive attack, at it makes you vulnerable to attacks. (Seems like explosive attack occurs upon holding the skill for about 3 seconds)
So instead of doing the full skill, cancel it before the explosive attack and quickly dash left or right.

Im not sure how much damage the explosive attack does, I w