But no matter how small the zone is, the point where the plane is to make a 90/180/270 degree turn is only in one zone. That means the ATC responsible for that

But no matter how small the zone is, the point where the plane is to make a 90/180/270 degree turn is only in one zone. That means the ATC responsible for that zone would see it. Are normal planes really doing 90 degree turns?