You don't base scoring off of how many bombers make it or don't make it. . . .You figure out what is reasonable for something to destroy and use that as your baseline for the rest of the stuff.
Figuring out what is reasonable involves estimating how many bombers will typically make it.
At some point, you have to make a judgement on how it will go.
For example, you make a design with P-47's, B-17's, and 109G's for 80 people. Do you make it (a) 20 p47's, 15 b17 formations, 45 109's? Or (b) 30 p47's, 10 b17 formations, 40 109's? Or (c) 35 p47's, 10 b17 formations, 35 109's? Or (d) 35 p47's, 15 b17's, 30 109's? Or . . . ?
What is reasonable scoring for (a) is not necessarily reasonable scoring for (d), and so on.
They are inter-related and subject to judgement.