Playing with these "box options" you have to remember several things:
- they are far from real options
- they are managed 100% internally by Oanda
- Oanda calculates itself the different probabilities and the associated the risk / reward ratio
- the calculations are made "live"

So 2 possibilities:
- Oanda's calculation are correct and in the long run they will win anyway
- Oanda's calculation are incorrect and there is an edge that you can get: if it so, Oanda will find it out at some point and will correct the "problem".
So even if you are able to find an inefficiency aftern several hundred or thousand of hours spend analysing the box options, Oanda can removed it in a blink of an eye and you are back at the start.
Of course you can always hope that you will be the only one to find the inefficiency and that Oanda will not notice it. But I think that the risk / reward ratio is not in your favour for this matter.

So my main point is that IMHO it is not worth to spend many hours to master a matter where the rules can change any second.