Can someone please explain the combat runes

[Totoro]

It's hard to believe the Luck rune trigger chance is only 10%. For me it seems to trigger like every other time.

And how does the medal that increases rune effectiveness by 10%/20%/30% affect runes?
Does the highest medal make attack rune give +50% to base attack and give luck rune 40% trigger chance?
Or just +26.666% to base attack and 13% trigger chance.