We need to always do research when we invest, different casinos give different payouts and options about your investment, besides you need to research how much you could expect to profit form your investment.
I also love investing but seriously I am telling from my experience that never go with the advertised house edge, I mean don't just invest in a casino or dice site because it has higher house edge and you will earn more I have been a investor since an year now and I always look for sites that have more wagered and more players.
Personally I feel rather than putting high bets I will increase that amount in investment.
You are correct, In gambling high bet amount or low bet amount both are a risk, because we don't know that we will get returns or not. But in investing, we will get a minimal amount of returns at the end of the month.
A user in the forum is running an investment in five different casinos and publishing his monthly gains and you are correct the most important factor is the size of the bankroll versus the amount wagered in the month.
Yes I am also following his thread, he made 5 BTC investment, And he got around 10% of profit in last 2 months. But in investment we need big bankroll otherwise, the profit will be very less.