I use electric netting (different to an electric fence) that is 48" high. Mine fly up to a 5' high roost so they can easily fly over it if they want to, but it's generally not a problem. But there can be issues.
When I have a bunch of cockerels going through puberty in there, I sometimes get some outside. When one is losing a fight and is trapped against he netting it goes vertical to get away. Sometimes it lands outside the netting and does not know to fly back in. On really rare occasions I might find a hen outside. She was trying to get away from an amorous rooster and went vertical.
I've found two things to help with this. Avoid sharp corners in the netting. 90 degree corners are OK but don't go sharper. That way they can usually get away without going vertical. One time I set it up with a narrow corridor between the coop and the open area, maybe 10 to 15 feet wide. I found three cockerels out that day. They could not walk past each other in that corridor without it becoming a fight. When I reconfigured it to a wide open space with open corners any escaping became pretty rare.
Yours have learned to fly out. I don't know if electric netting will change that or not. The netting not having a top rail to land on could help.
What would happen if they DID land on the top (electrified) wire? Would they be able to get off again????
For the circuit to be completed and them get a shock they have to touch a hot wire and a ground at the same time. Other than the bottom wire that touches the soil the horizontal wires in the netting are your hot wires. With netting the soil is your ground. Their feathers insulate them. For your chickens to get a shock they would have to touch a hot wire and the soil at the same time with their feet, comb, wattles, or beak. That is not gong to happen if they are up high. Something you might observe is if their feet are on the soil and they peck near the base of the netting to eat grass, they get a shock when their comb, wattles or beak make contact.. Mine jump back and up and squawk when that happens, then go back to grazing. They learn to not peck at the base of the netting.
The current is not continuous. It pulses about 50 times a minute. If it were a continuous current you, they, or anything else could not turn loose. That would be bad. But since it pulses you and they can turn loose, and will before you have time to think.. That pulsing is what makes it so safe.