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It was actually 13 satoshi/byte on a 2 segwit input to 1 segwit output tx. The fee didn't change when the amount to be withdrawn was modified, so my guessing is that the tx size is not taken into account when doing withdrawals. I understand that it's impossible to use a 100% accurate fee when the site is dealing with many deposits and withdrawals and the process is most likely automated, but I also think there's room for improvement.
It's not really fair to pay 4 times the actual tx fee, and even if I understand that doing that many withdrawals with different variables could lead to the site loosing funds on the long run, fees could be a little bit more dynamic...
Sorry, I mistyped in my original post. I meant to say that it should have been 20 satoshi/vbyte (or 5 satoshis/WU) which I bet it was. Certain aspects of transaction data are weighted differently (hence the switch to WU) since the Segwit soft fork and it is no longer accurate to use satoshis/byte. Most people use it to refer to satoshis/vbyte now which is reflective of what is actually happening.
Crypto-Games could have 1 BTC inputs, and 0.001 BTC inputs. Withdraw size wouldn't really matter in that case, but of course the smaller inputs do need to be spent (and go towards smaller withdraws).
Let's say that Crypto-Games was lacking on large inputs, and needed to use 11 inputs at around 0.01 BTC each to pay a 0.1 BTC withdraw. Would you consider it more fair to have some users pay fees for a 1180 byte transaction, and other users pay for a 280 byte transaction (2 inputs 2 outputs)? Would you personally be willing to pay 4 times the fee just to get the same sat/byte as other users?
Welcome to withdraw fees from any site that isn't a personal wallet that you have full control over. If they don't subsidize withdraw fees or offering batching as an option, this is usually what you end up with.