Flightzones are fluid and everchanging, they are not usually a perfect circle. This is because of something called draws. The more the dog works the flightzone and reduces the draws, the more circular the flightzone will become, making the stock more neutral.

When a dog works the flightzone, both the dog and the stock will settle. There are some physical signs that a dog will show that they are working the flightzone. Their tail will relax and they will tip their nose in and out. They tip their nose in and out because they are reading and adjusting to the stock. There is no set distance for a flightzone, it will all be in relation to the dog, their presence, and how the stock perceives the dog.

If a dog has the ability to work flightzones, they will be able to work a variety of stock in a number of different situations. Different dogs will have a different flightzone on the same stock. Moreover, the same dog can have a different flightzone on the same stock at different times of day. A dog that is working the flightzone appropriately, in time will be able to minimize the size of the flightzone.

Temple Grandin has a wonderful illustration that describes working the flightzone, including point of balance, and how to start and stop the movement of an animal. Here is the link to her page: FLIGHTZONES.