A sundae is not a scoop with sauce on it. It is a structure, and structures need room. The reason most shop sundaes look worse than the photograph on the menu board is not the recipe. It is that they were built in a cup that had no space left by the second layer.
Room to work
The 12 oz paper ice cream cup is a large portion that holds a loaded sundae or a triple scoop. What that buys you is not a bigger serving. It is headroom, and headroom is what lets a sundae be assembled in visible layers instead of compressed into a mound.
Try it once with a standard counter cup and once with this one, same ingredients, same order. The larger cup version looks like something you would charge more for, and it is the same product.
Build from the bottom, not the top
Sauce first, then ice cream, then the next sauce, then toppings. Sauce poured over a finished mound runs down the outside and pools at the bottom where nobody can reach it, which is why the last three mouthfuls of a badly built sundae are plain ice cream.
Layering also means the customer sees the structure through the side of the cup as they eat, which is the part they photograph. A cup with no headroom cannot be layered, so it never gets photographed.
Where the size stops making sense
This is not a general-purpose upgrade. A single scoop in a 12 oz cup looks lost, and a customer who paid for one scoop and received a mostly empty large cup feels short-changed even though they received exactly what they ordered.
Reserve it for what actually needs the volume: sundaes, triples, anything with a serious topping load. Single and double scoops belong in the smaller sizes, for the reasons set out in portion control with 6 oz cups. Using one cup for everything is how you end up giving product away at the bottom of the range and disappointing people at the top of it.
The lid decides whether it survives
Everything you just built sits above the rim, which rules out a flat lid entirely. A dome exists at this size and it is not optional for a takeaway sundae, it is the thing standing between your layers and a flattened mess in a delivery bag.
If most of your sundaes are eaten in the shop, you can skip lids at this size altogether and save the line. If any of them travel, the profile question is settled before you start, and we went through the reasoning in dome or flat lids.
Stocking it
Cases run a thousand. For a shop where sundaes are a menu item rather than the whole menu, that is a long time, and it means the large size can sit on the shelf without pressure while the standard sizes rotate underneath it.
It runs in solid colors, polka dot prints and striped prints at the same case price, and a print at this size is doing more work than at any other, because the sundae cup is the one that gets photographed. The full ladder sits in the ice cream cup range.