John, yes, I'll try to pick off some of the parts of your question there. First of all, on U.S. unit development, I'll just make a macro comment overall. There is still a very healthy demand out there among our franchisee base for unit development. I've highlighted some of the challenges in the near term of getting these stores open. But when we take a look at the profit of the 4-wall profitability at the store level and the resulting cash-on-cash returns for Domino's, which is ultimately what drives store growth, it's still very, very strong.
And as we continue to dust off our models to take a look at what the U.S. holding capacity is for Domino's stores, we continue to be very bullish about that holding capacity. I've talked about 8,000 store potential in the past, and we believe it's at least that, if not more, as we continue to dust it off.
When we open new stores, a significant portion of those are fortress stores in that they do take some number of addresses from existing store service areas. When we take a look at the impact that, that has on the comp, I have spoken in the past about that being 1 point, 1.5 points or so. If you take a look at the third quarter, it was about 1 point when you look across the system and a bit higher than that on the corporate store side because, to your point, we have been a little bit more aggressive in terms of percentage opens off the base, but also basically every store we open in our corporate store business is a fortress store.
But when we take a look at what the cash-on-cash return expectations are for those openings and we look at it, not only on the individual new store, but we look at it on the impact of the store cluster that, that store is a part of, we still see very positive returns on those stores, and that's why we continue to be aggressive in the growth of our corporate stores.
So it -- fortressing is going to continue to be a key part of our strategy, John, and I haven't seen anything in the quarter that gives me any sense that we should be slowing down. There is still a lot of opportunity out there to continue opening Domino's stores around the country.