5* sl for LOL

I’m practicing with sl in LOL and I’m not getting the longer enrage timer with 18% attack synergies. Isn’t this the magic number for him? Anyone else not getting the longer enrage timer with 3 synergy champs?
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Here’s what I’m using. All the synergies are 6% attack
This champ alone has 2k attack. Is it enough to get longer enrage timer?