The referral system is a multi-chain network that requires intense marketing and that bookie that offers such betting always gives a good percentage payment on each referral but again if your referees are not active you may not earn so much as most bookies do so to discourage cheating.
I agree with you in this one. It's not about the total of referred gamblers but it is all about how active they are in gambling on the site that op will refer. Well, if op have lots of gamblers to refer and most of it are active then op can get commission from each of the referred gamblers. I would suggest sportsbet.io as they have a nice referral system.