You just get double the space per referral, but you can not exceed the 18GB limit. That means you can get to 18GB faster, with fewer referrals. But I don't kno

You just get double the space per referral, but you can not exceed the 18GB limit. That means you can get to 18GB faster, with fewer referrals. But I don't know if it works retroactively for refs you already have.