Put some taller posts in the center and run a ridge down the middle to raise the top covering high enough for you to walk under. You will need some way to shorten the span of the chicken wire anyway. If you run chicken wire or any material across a 17' span it is going to be sagging down to the ground very soon.
Even if you manage to stretch it taut, you will be faced with the same problem that some here have written about over the past week, where they provided absolutely no method of supporting a covered run that gets covered with ice and snow and now it is on the verge of collapse.
So yes, I agree you should cover the whole run if you need to to protect your birds from predators from the sky, but do it in a way that it won't collapse after the first ice storm. Keep a number of 2X4's handy over the winter to simply prop it up. It's a lot more rewarding than doing nothing and then complain about it later.
Wayne