It ignores 25% of the armour critical modifier.
What's the max armour critical modifier? 10? 15?
1/4*10 is 2,5 - rounded down 2, rounded up 3, 1/4*15 is 3,75, rounded down 3, up 4.
So you're getting bonus +2/+3/+4 on roll and +2/+3/+4% crit chance when hitting BA/CAMK2 guy, even less when hitting worse armor. I'm sure there are a lot of better perks out there :F
Compare it to the epic HtH Criticals, let's say it gives +4 on roll, so Hit The Gaps is like 4/25 of HtH Criticals, not even always, only when you hit well-armored guys.