Chickens don't do logic logically. A 5 foot tall fence with 8 foot tall fence post looks like an 8 foot tall fence. Almost all my chickens could clear my 8 foot fence (3 feet of 1 inch chicken wire topped with 5 feet of 2 inch chicken wire) in their sleep but chickens like every animal including humans are lazy and they almost never went the whole Monty. The fact that my red ceder fence post for my 8 foot tall fence were 12 foot above ground giving the appearance of a 12 foot tall fence didn't hurt.