I am not against a house edge, it is absolutely fair to charge a fee for providing service, but your house edge seem to be pretty high to me. That is why I am asking to provide more details on how exactly you calculate payouts and how much you keep for yourself.
Blockchain (or DAG) based business is all about transparency. Without transparency why bother about these technologies?
You keep using "house edge" as if this was in relation to casino gambling... You are using the wrong term. It is NOT a house edge. A house edge is the theoretical "edge" that the house has based on mathematically provable probabilities over an infinite series of events.
This is more like sports betting... and the risks involved offering odds on the result of a sporting event.
Given that there are so many factors outside the control the guy running this service... and the result is not likely to be "truly random" like casino games are supposed to be, I would suggest that he has basically done a quick "risk calculation" based on historical data/current events/magic 8 ball... and has created the options as he deems appropriate.
Essentially the same way a bookie will calculate odds on a sports result...
Think of it this way... Brazil vs. Scunthorpe United in a game of football... it wouldn't be entirely unexpected that the payout for Brazil winning would be something like "$1.01", in which case, you'd need to wager $100 to win $1.... much like whatever option you were looking at... betting 1 GB to make 0.8 GB... sounds like the "bookie" decided that was the more likely outcome of the two and adjusted the payouts accordingly.
It is in fact a house edge, you can call it what ever you like, but these fees are so high that professional traders are probably unlikely to want to use the service. For me, the fees are far to high for me to use it, although I would definitely use it if reasonable fees of 0.1% or so were levied.