re: Design ratio
Take the design ratio for example:
DR = (max payload) x (max altitude with max payload) x (range with max payload) / (runway requirement at MTOW)
I'm of the opinion that this ratio should be maximized whenever possible. This means it can take off from 98 percent of the airports in the world carrying a large payload, deliver it to a very distant location, perform the zoom maneuever, then reverse course and fly back to its airport of origin (whether or not the zoom maneuver was successful).