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While testing this stuff it definitely feels like the explanation for offset in the mod tools is completely wrong. I always expected the hit area to be a half circle at 1 based on that, but instead it seems the offset just moves the entire possible hit area forward (or backward with a negative value). With a value of 1 all targeting is now centered around what used to be the edge of the old scatter area....
Light green ellipsoid part is calculated scatter centered around the targeting circle. Blue ellipsoid overlayed on top is an offset moving the entire targeting area forward.
If we forget for a sec the other factors like elevation difference and the tendency or not to overshoot the formulas you provided do not justify an ellipsoid shape. The only why one can get an ellipsoid shaped is if the probabilities of distance and angle scatter are linked, and a high distance scatter shot will have a low angle scatter and vice versa.
If the angular scatter and distance are statistically unrelated (and i have no idea if they are) one should be getting one of the following shapes depending on weather angular scatter uses distance to target to be calculated, or distance actually traveled:
If the length scatter and the angular scatter are actually related and the shape is actually ellipsoid what distance is used to calculated angular scatter would effect the shape. If the angular scatter use distance actually traveled the shape would be symmetrical over the X axis.
If angular scatter use distance to target then it overshot would tend to scatter angularly less while undershots tend to scatter angularly more and the shape would me more egg shaped..