(with your site, i. e. , my small investment was too diluited)
It doesn't really matter what percentage of the bankroll you control.
All that matters is how often the bankroll gets "turned over".
If the bankroll is 5 BTC and 10 BTC is bet each day, you can expect to make 2% profit per day.
If the bankroll is 5000 BTC and 10k BTC is bet each day, you can still expect to make 2% profit per day.
In those two cases, your 3 BTC investment is going to have hugely different levels of "dilution", but it doesn't make any difference to your expected profit.
In other words there's not much point being 50% of the bankroll if nobody bets on that site.