Rain of Stones?

[Bastiat]

Quick question about AoE:

From what I can gather these are all of the possible AoE values:

BF, 25, 15, 12, 10, 9, 7, 6, 5, 4, 3, 2, 1, 0

0 - Presumably impacts caster only
1 - Presumably impacts the square the caster is in only
BF - Limits noted in thread, otherwise most of the BF

What is the AoE for values 2-25?

Is it the radius around the caster (150 squares for an AoE of 5)?

The diameter (39 squares for an AoE of 5)?

For an AoE of 5 is it a 5x5 square centered on the caster?

Is it literally 5 squares? And if there are 9 squares around and including the caster, are the actually 5 impacted squares a random draw from the 9 possible squares?

Also, does anyone know what the total area of the battlefield is?