XFX rx 580 8gb base model - ETH - ethminer benchmark lower than expected

So my background is that I make web applications and do not know much about hardware.

I bought like 12 XFX rx 580 8gbs assuming they would get a hash rate of 24+. I am getting a max of 20. Does this sound normal? I am not the best searcher in the world, so apologize if I overlooked a post with this answer.

Thanks in advance.