Seems to me that you would have less chafing with a clove hitch. Those two sheets are making some pretty sharp bends there exiting from under that single loop. The pull on the two bitter ends of a clove hitch would be in straight vectors along the strongest tensile axis of the line, and also produce the least amount of deflection, friction, and chafing as the two sheets would exit from their respective sides of the knot.
But that's just my opinion. I like clove hitches.
I just replaced my two sheets with a single one this past week and debated about using the cow hitch or the clove. I then decided on the constrictor knot which is basically a clove hitch with a slight modification to prevent any slippage. Look it up on line. When it comes time to take the sheet off in the winter, I may regret having used that knot since it's difficult to untie.