Can We Fix/Change The Crit System For Adc's?

I was asking, because as of right now, it feels a little too unreliable. I go to last hit a minion, then minion is at 1/4 health remaining, and that one attack crits. The minions dies. All is well.

But now, I'm trying to push a wave, but still trying to get the cs that I need. I go to damage a minion, and I crit. The minion now has 2 Hp, left. My scumbag minion ks'es it, and I don't get the gold (ks'ing n00b caster minion doesn't know how 2 pley. uninstall plz)

Same minion wave. I see another minion with about 1/3 health. I go to kill it, expecting another crit. I don't crit. The minion now has 2 Hp left. My other scumbag minion ks'es it, and I, yet again, don't get the gold (same ks'ing n00b melee minion steals all my minion kills. toxic af, uninstall, melee minion, plz)

And maybe this has just turned into a Vayne rage post, but I just don't understand how if her first aa hits me, it can deal about 300 damage, w/o criting. But the very next aa she hits me with, crits and steals half of my health. Just one aa.

Maybe the last point is just stupid, cause i suck as Ashe, but the earlier points are the reason why I'm saying this.