Yes that is correct.
Dooglus could you emphasize on what you have in mind by clearing it part by part?
Yes. I deposit 1 BTC, you credit my account by 1.25 BTC, and show on my account page:
balance: 1.25 BTC
held: 1.25 BTC
Then every time I bet 0.1 BTC, you reduce the 'held' by 0.01 BTC. So I bet 0.1 BTC, and let's say I double my money. My account then shows:
balance: 1.35 BTC (I doubled the 0.1 BTC I bet)
held: 1.24 BTC (you reduce the held amount by 10% of everything I bet)
If I wanted to, now, I could withdraw my balance minus the held amount: 1.35 - 1.24 = 0.11 BTC. Making any withdrawal ends the bonus, so you reset the held to 0 and take 1.24 BTC off my balance. The player can chose whether he wants to play through the whole bonus or stop part way through. He'd be silly to stop so soon, because he loses so much. But maybe later his balance is up to 3 BTC and he only has 0.5 BTC held. He might decide then to withdraw the 3 - 0.5 = 2.5 BTC that he's allowed to withdraw, and give up on the rest of the bonus.
That's how it worked on
https://strikesapphire.com/ when I used to play there, and it seems very fair. See their T&C page for the gory details.