It should be also confirmed with the information under the VIP lounge as quoted below:
On top of that, we now offer you dynamic level up rewards which is 12.5% of house edge!
In a simple explanation, the higher house edge of the game you play, the higher level up rewards you will get.
Oh wow! Interesting information! I don't really play there, so I wasn't aware of their VIP System. Yeah, You are correct that most casinos have a fixed amount to reach VIP levels and a fixed level-up bonus. Interestingly, Duelbits share 12.5% of their house edge. I am curious how it works. For most In-house games, House edges are low. I've just checked Duelbit's In-house games that I like most. Dice and Mines both games have a 1% house edge. But I am surprised that their roulette game has a 6.66% House edge, confirmed by their live support.
So, Let's say someone wagered $1000 in Dice games. He should get $1.25 as a level-up bonus. At the same time, If someone wagers $1000 In Roulette games. He will earn $8.325 as a level-up bonus. That's amazing. I hope gamblers will find it interesting. At least, I find it quite fascinating. I don't think I've seen something like that on any other platform.
Another thing is, Their live support has to more time answering their users why they did not get the same bonus as their friends.