I've got a 6 foot fence. My seven month olds flock of eight consists of 4 pairs,
in order smallest to largest there are 2 Hamburgs, 2 Yokohamas, 2 brown sexlinks and 2 Rhode Island Reds.
I've seen all of them sitting atop the fence except the RIR's at one time or another during the past month.
A few months ago Ruby, my flightiest Hamburg, had gone over the fence into the next yard and was evading the
neighbor's Labradors. I was watching as the two of them closed in on her and she went airborne.
She cleared the fence by at least 3 feet, mavbe 4, as she escaped back into our yard.
I think most chickens can get over a six foot fence. They just don't know it, have no real desire to escape,
and would prefer to hang with the flock. Ruby is the only one who has actually gotten out and when she
was, spent the whole time cackling and trying to get back in. Except that she is too stupid to realize she
could fly in, just as she flew out. So she cackles unhappily until I show up with the bucket of scratch and her
flockmates and lure her back in through a little gap in the fence.
I think they just like to flap every so often and sometimes they surprise themselves at how effective it can be.
I'd put money on them getting over the 6 foot fence in time.
4 foot is not a fence for them, it's a jungle gym.