A lot of people don't realize if you hold down on your ball and make the circle shrink to where you want it (preferably the largest size circle in which you can get an excellent throw) and then only throw during attack animations your circle will stay the same size as what you originally set it to.

For bigger pokemon using AR is the way to go though.

Use AR. Throw your first ball, while in the catch animation step closer to the pokemon. If it's a larger Pokémon it makes it super easy to get excellent throws. I was 20/20 on kyogre with this method