Auto exchange vs direct mining

Since the halving I've switched to unminable to convert ETC and ETH into RVN. According to whattomine.com with I am more profitable mining other coins in $ so in theory I should get more RVN coins if I was mining directly. But according to the mining calculator with the hashrate I had, mining straight into RVN, I should yield more coins About 20% more

How is that possible, do I loose that much in exchange fees?

All this assuming 0 on electricity cost