I'm not sure about that. Assuming no covariance (e.g., two hands on two different tables) my first educated guess should be 141.414141...% for no risk increase.
If there is no covariance then the bets should be the same size since there is no increased risk. This is like playing to a joint bankroll - each player can spread the same amount even though they are sharing the same money.
But if you are playing two hands on the same table, the result is covariant with the dealer's hand...So the ratio would have to be less than it is for 2 hands on 2 tables.
That's exactly right. The optimal bet will be somewhere between 1 bet and 2. We can use the Kelly formula to find out the optimal bet for any number of hands we want to play. This will ensure that we are not adding any extra risk to our betting system by spreading our bets. For a $13,300 bankroll and a 1% edge:
(Bankroll * Advantage) / Variance = Bet
($13,300 * 0.01) / 1.33 = 133 / 1.33 = $100
If we want to play two hands at the same table then our variance will change. As you pointed out, it will be greater than one hand but less than double. Each hand you spread to (at the same table) will increase your variance by about 0.5. That gives us:
Two Hands:
($13,300 * 0.01) / (1.33 + 0.5) = 133 / 1.83 = $72.67 for each hand (total bet = $145.36)
Three Hands:
($13,300 * 0.01) / (1.33 + 1) = 133 / 2.33 = $57 for each hand (total bet = $171)
By spreading to two hands we can increase our bets while maintaining the same level of risk. The numbers above show a 72% increase for two hands and a 57% increase for three, although most people will round them to 75% and 50% for simplicity. That is where ZG gets the 150% rule.
Alternatively, you could spread to two hands of half your usual bet (2 x $50 instead of 1 x $100) and have less risk on the same expected return. This can be a great way to reduce your ROR without cutting into your profits.
-Sonny-