How much Hibiscus

So I am brewing the hibiscus mango blonde from zymurgy I am doing 3 gal. They say add 13.3 oz in secondary. That seems like a lot!  I was thinking about just adding 4 oz to a 3 gal batch. What ya think

I would reduce the amount 40%, the same as your 3 to the original 5 gallon batch or about 5oz