As you know the Bitcoin fees are quite high at the moment due to the Lightning network not having been deployed yet.
The actual fees that your Bitcoin core wallet pays to the blockchain are controlled by your bitcoin.conf, not the plugin.
In your coin adapter there is some text about this, I’m pasting it here:
This withdrawal fee is NOT the network fee, and you are advised to set the withdrawal fee to an amount that will cover the network fee of a typical transaction, possibly with some slack that will generate profit. To control network fees use the wallet settings in bitcoin.conf: paytxfee, mintxfee, maxtxfee, etc. Refer to the documentation for details.
So you will need to configure a sensible amount of fees for a single transaction, depending on how fast you want it confirmed. The withdraw transaction is from one address to one address. You should set this in your
bitcoin.conf. Then, make sure that the withdrawal fees set in the plugin are at least as high as this, or higher.
You can estimate a sensible value for the current time period from this webpage: https://bitcoinfees.earn.com/
Also take the time to read this: https://support.earn.com/digital-currency/bitcoin-transactions-and-fees/how-do-i-calculate-my-transaction-fee
Hope this helps.