Premium Rate is the portion of amount which exceeds the market price. 'Unit Price' is the average price calculated among major trades. An appropriate premium rate can help you set up a sensible price. For instance, if the unit price of the cryptocurrency is 30000 and the premium rate is 5%, the trading price will be 31500.
To make your offer more competitive, you could set up a negative premium rate. For instance, the current market price is 30000 and the premium rate is -5%, the trading price will be 28500.