Point-and-click abilities are weird

By this, I mean that they're coded very weirdly. They're SUPER inconsistent if they have a cast time. Thanks to this Vs Event, I've been nolifing Garen mid (it's super fun, try it. run grasp as your keystone, ignite and flash, and build )

But here's where the problem lies, yeah? His ultimate is unbelievably frustrating to pull off consistently. Sometimes when I ult someone, it doesn't matter if they flash/dash/stealth/blink/anything, they'll get hit. Other times, I'll ult someone and it'll cancel. I'll be mid-ult on someone in front of me, take damage, and it stops. They'll go over a wall, it stops. They'll flash, it stops. They'll go in to the Fog of War, it carries through.. or sometimes it stops. This absolutely works with Master Yi, as well. Alpha Strike will sometimes follow someone through a flash/dash/blink/escape in to the FoW, but sometimes (and usually in those clutch moments), it won't! I don't understand. Does anybody else notice/experience these moments? I'm sure that if you're the target and it cancels, it feels pretty good - "Phew, safe!" - but it feels terrible to play.