I agree that we must define what it “open” to our players. Of course, that’s tailored to each players abilities, but you mentioned 60% 3pt shooters. If you define “being in the bubble” as the defender’s ability to touch the ball in your shot pocket, then some 3pt shooters are open when a defender is outside their bubble (they can shoot without altering their form or their normal rhythm. However, some shooters must “step in” to their shot which means they need a little more space. A more general rule would be if when you catch the ball, your defender still has at least one foot in the lane, you have time and space to shoot your normal 3pt shot.
Regarding playing 3+ feet outside the arc, practice stepping toward the rim while the pass is in the air. Push off with the outside foot when the pass is made. It will square the shooter to the goal and their momentum is toward the rim. The passer should be leading the shooter to the inside (not necessary, but very helpful) because the shooter’s defender has allowed the space.
Whenever your 3 point shooters cut, they should try to backscreen any teammate that is 1 spot away from the ball. That way, they’ll be shaping-up to shoot after screening. If they find themselves 2 spots away from the ball, immediately set a Baby Pin Screen for the teammate who is one spot away and then shape-up for the 3 pt shot, or cut to the basket depending on how the defense plays.
If your 3 point shooters will obey the rules of cutting (Pass & Cut, Read Line Cut, Dribble-At Cut) and add the above two actions to their game, your team will have lots of player movement, threats on the rim, two different kinds of screens, and your best shooters will be more available.