Depends on when you go. If you show up during lunch/hour when the line is getting long they absolutely will over scoop. It isn’t worth it for them to slow down the line when every customer asks them “can you scoop more” at every single step. They just over scoop to keep people quiet and keep the line moving. The difference is about 2x an online or off-peak order, and about 3x a late night order (hour before closing). Just my experience though.
I feel they are less likely to skimp you if they are face to face with you/you signal you are willing to pay extra for extra (whereas on the ticket as an online order they build, they might miss it)