We also still need the ranges and angles on the Yuuko-Howitzer. But, assuming it has a range of 1ly and an angle of 30deg:
Let’s do the math.
Use the tangent function to determine what the short leg of the right triangle, small angle 15deg is.
We can use tan(15) to determine that number is 0.267ly. This is the radius of the explosion at maximum range. Multiply by 1ls (300,000km) and you get 80,384km as an explosion radius at maximum.
Needless to say this is gigantic. And since the ASA is a pretty old submission, let’s not use it as a reference point. Remember that this is all packaged into a tiny missile, Tier 7 in size, when the Eikan has a gigantic front section purely devoted to firing these bursts.