I feel very confused about the greeks analysis for the broken wing butterfly strategy.
Let's say for the stock ABC, we enter into a such strategy: we long a put option with strike $k_1$ and another put option with strike $k_3$，and at the same time short two put options with strike $k_2$, where $k_2-k_1>k_3-k_2$.
Then what I read tells me that this position is possibly a net debit or a net credit when starting with. Intuitively, if $k_1$ is too low, then the strategy should be a net credit. Intuitively, if the stock price is above $k_3$, the $\Theta$ should be positive since I profit from time decay. At expiration all puts will become worthless. But if $k_1$ is not that low, I can imagine it would be a net debit position when entering, then the $\Theta$ would be negative since I will lose money from time decay.
How to understand such behavior of this strategy. And another confusion is, if I enter the strategy with net debit, I will have two break even price; but if I enter with net credit, I will have only one. This also seems strange to me. So what determines if I enter with debit or credit, and how to understand the behavior of this strategy? Thank you so much!