My SM's philosophy is if they're making a purchase, we'll give them one no problem - any size. If they're freeloaders, they're getting a tall - and they're gonna wait so we put them in line with all they paying customers. if they give attitude, we keep moving it back
One of our shifts who just transferred makes 5 tall cups filled to the top with ice, adds water and then leaves them just below the hand-off plane to quickly give out if requested. If their ice is melted and they ask for more ice - he tells them it's free and if they want ice, they have to wait till he finishes all his drinks in the que ... they usually walk away.