There isn’t a way to enforce a single global cap for the entire event. The Event Capacity field is informational only, and the system enforces limits only at the fee level. The only way to limit event capacity is by setting each individual registration type with a limit. However, if you set these all to equal numbers, you may miss out on maximizing the total number of registrants. For example, if you have college students and there are different prices for each grade level, but you set an even number for each registration type for your max overall capacity of 100, you may miss registrants if you actually have 50 freshman, 20 sophomores, 20 juniors, and 10 seniors. Difficult in situations where you don't know how many from each different group type may register.