Yes I understand your point and as I said, I've included that you need to pick a type of seats you're selling out. For a incremental change, which I assumed was the case and I later explained too, you don't have to lower the price to sell the couple of extra seats you built. Maybe afterwards you don't totally sell out, so the next time you invest you don't include that type of seat in your options.
I did not give advice on what is the best formula to calculate ROI. I was just giving some help to decide which seats to build first, and added a simplified theory with some conditions to help in that decision. That's all I wanted to do. It's all nice to be able to calculate your actual ROI in all cases, but I think that's not necessary when deciding what seats to build.
So if you're selling out both your Luxuy boxes and bleachers, luxury at $600 per seat and Bleachers at $15 per seat, you suggest just building more Luxury? I would assume not, but then at what point would you? Do you have a calculation for that? You need to strike a balance in ROI and predictability, and I think it's hard to calculate a point where one is better than the other. I suggest just looking at ROI the way I proposed for incremental increases in seats, and when the ROI is close then go for the more expensive seats.