Does that work in casinos too?

Can you go to a roulette wheel and not put all your money on red. Then if you lose, you can make a profit from the bit you didn't lose.

Stupid analogy, but appropriate I think.

How do you make such huge returns?

I am very interested in your website and investment proposal. I have an extra 20BTC that I have been looking to put into an investment vehicle. To be honest though, I would probably like to diversify my investments and based on your proposal, I would only feel comfortable transferring 7.5BTC into your website. If this works for you, I'd love to start immediately. In order to gain a trustful relationship between us, I would only consider investing if you would be able to transfer .5btc into my wallet and I will return it on top of my 7.5btc deposit. If this is possible, please let me know and I will give you my wallet address. If this is done, I would be more than willing to send 8btc back to you immediately after I see the .5btc, so I know that you are a legitimate HYIP.

It's zero risk if you adopt this simple strategy:

"don't send them your coins"

I guess my sarcasm isn't very clear.   This is very clearly a Ponzi type of scam.   You can't insure 10% a month with Forex.   That is a highly leveraged market.   Leverage goes both ways.   Most people don't know anything about Forex or how to trade currency pairs.   Clearly they are counting on that.