From my experience, slippery bastard opponents only have advantage on the first attack, that is, when I have to learn the hard way that I cannot lock on. Once I learn this, I am ready to adjust.
My first tip is to get better at free aiming, common sense I know, but this leads into my second tip, which is the best advice I know of regarding this.
PIB! Paint It Black! If you can free aim well enough to swipe the crosshair across their head it will paint their head, boom, headshot. If you are quick enough you can paint them quicker than they can free aim. Especially at distance, a slippery bastard does not stand a chance, I will paint him, or better yet, if he is more far out than that, hit him with the rolling block. If you have dynamite arrows unlocked, then you can hit just close enough and they will die a fiery death from the blast radius.
Also, Keep in mind they will have to refill their deadeye. On your mini map, wait until they become a dot again, and not an eye, showing they are not in dead eye anymore. That is also an opening.
Hope this helps!
