Shield Charge + Fortify Support doesn't apply properly?

If I combine Shield Charge with Fortify Support to get fortified, it sometimes doesn't apply. I tried to add in Increased Area of Effect Support to see if I'm just not hitting anything, but it didn't really do anything.

Checked gem requirements -> fine, but I changed to lower level gems anyways for testing

Then I tried it out on some mobs in Act 5 and to my surprise I immediately got 20 Foritification stacks. Is there some rule that Fortify won't always apply to higher level mobs? Is it because of the mobs' evasion?