Spot: Loss when converting larger amounts?

Hello. If I use market rate to convert 4 BTC to USDT and immediately back, the success rate is between 96% and 100%. When I try to do same conversion with only 0.4 BTC, the success rate is mostly above 99.99%

Why is that? Is 4 BTC too much so it creates many lossy market orders? (I use tradePart 100% and 10% and use SELL with quantity of tradePart * full amount and BUY with orderQuoteQty of tradePart * full amount)

The reason is because when you attempt to convert large amounts (eg. 4 BTC) using a market order, there is less chance of there being enough liquidity at the exact current rate as there is when executing a market order with lower volume (eg. 0.4 BTC). You can always take a look at the orderbook and see how much BTC is available on the market at each price level.

yep. or just google “slippage”