Please help clarify this Goldpool synergy

The synergy states that
“All champions gain 1000% special attack rating”
How is special attack rating different from base attack rating?
The damage difference between with and without synergy is not even 10%. See below. I tried a few different champs but the results were the same.



“All champions gain 1000% special attack rating”
How is special attack rating different from base attack rating?
The damage difference between with and without synergy is not even 10%. See below. I tried a few different champs but the results were the same.



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Strange...
Dr. Zola