EWBF's miner actually took 5-6% DevFee instead of the stated 2%. I checked the log file out of curiosity and counted all accepted vs DevFee:
GPU0 1703 accepted
GPU1 1772 accepted
GPU2 1791 accepted
GPU3 1723 accepted
Total: 6989 accepted
DevFee: 362 instances
362 / 6989 = 0.05179567892402346544570038632136 = 5.1%
On a second run I got the following:
Total: 6159 accepted
DevFee: 347 instances
347 / 6159 = 0.05634031498619905828868322779672 = 5.6%
I was doing around 1800 sol/s with EWBF and around 1700 sol/s with NiceHash's Excavator. So I stopped using EWBF since there's no difference running Excavator over this.
You are a miner and i think you must know what's mean mining difficulty.
If the difficulty of the devfee pool is lower than the difficulty of your pool, than the number of devfee shares will be above 2%, only because the cost of each devfee share is lower than the cost of each share of your pool.
Try to run miner on this pool:
http://dwarfpool.com/zec and use the port with low difficulty 3334, wait for about an hour, and then calculate the number of shares.
And yes of course you can use --fee 0 if you wish...