Lets say I open a first position for 10usd then second position I want to open is 20usd (while the first positio is still running)
I select 20 usd in the exchange for the second position and the exchange opens a position for 17 instead of 20 for example..
I am using limit orders and is not related to the minimum amount to be traded
I think you confused with the exchange balance valuation and valuation while buying and selling. The small difference occurs due to the volatile prices on the market book so let's say if you choose to sell x amount of coins at 91K instead of 92K then you will recieve less fiat but the trade will be executed instantaneously. So just make sure you enter the right price while buying and selling to reduce the amount closest possible value.