To configure the buy amounts as a percentage of your balance, you can use percentage buy amounts in the Base config settings.

This value is a percentage of your total assets on the exchange or, if configured, based on the 'Maximum amount allocated'. If this value falls below the Minimum amount per order, your trading bot will use that value instead.
​
Since the trading bot looks at your total assets on exchange or 'Maximum amount allocated', we do not recommend using values higher than 95 percent to ensure your trading bot can place new orders.
​
When having reserved positions, your buy amounts will be smaller than the shown percentage buy amounts.