Leeway has been in WoW since Vanilla and remains in WoW to this day in the exact same form, unchanged. The only thing they did was normalize Tauren hitboxes years ago.
Here is the Leeway formula that has been in use and unchanged even in retail.
Leeway formula:
Melee attack: MAX(5, SourceCombatReach + TargetCombatReach + 4/3) + IfSourceAndTargetAreRunning(8/3)
Ranged attack: SourceCombatReach + TargetCombatReach + AttackRange + IfSourceAndTargetAreRunning(2)
AoE: TargetCombatReach + AttackRadius + IfSourceIsRunning(2)
I ssugest you go read this thread, check out the post from Velenno, he provides links and videos to elaborate
What is it with people in this day and age that claim some bull, never back it up and continue to perpetuate said bull despite all the evidence against it?