Question about Blast rain and Point blank Keystone

Taking point blank keystone makes your projectile attack damage deal less as the projectile has traveled. So, how does this keystone interact with blast rain? Does the distance count from the actual blast to where I click to use skill or from the actual blast to where my character stands?

From the blast to your position. So if you cast in in the middle of a pack the mobs closer to you will get the most damage.