Now, playing devils avodcate for the real life guys, it's...Lye-El!
In real life a 5 inch shell didn't do "progressive" it just went *BOOM* AND you had falling shrapnel to run into as it fell to the ground after it expended its energy from the burst.
That could be a source for the .303/ 5 inch hits...but then you would have to track the shrapnel as it falls and track aircraft interception with the pieces. Too much data for too little return. You could also incur hits from a shell that went off 5k over your head a couple of minutes ago and the dispersion field would be quite wide.
Now about a different tact. Might be too much added caculations though....Zones measured from the center point of the blast of a 5 inch. As you move out damage becomes less?
An experiment is in order, let me take this 5 inch shell into town and take up into the church tower to simulate an airburst....ok, got it.. Now when I hit it with this hammer I should be able to figure out the blast radius. Ok, here I go, swinging the hammer NOW!.............................
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$%#@! THAT HURT!!!!!!