I keep my spending btc in gdax till needed and I moved some btc to play with the Shift debit card.
Just a quote for selling 0.00164800 btc on coinbase.

0.00164800 BTC $24.31
Coinbase Fee $1.49
Total Payout $22.8

I see what your talking about, coinbase calls it a "Conversion Fees"
https://support.coinbase.com/customer/portal/articles/2109597

From what I can tell, its a "Conversion Service."  It looks like an add on fee for making it easy to trade.
Perhaps use gdax limit sell and ACH withdraw to avoid that fee.