Attacks Single Out A Target?

[COLOR="Green"]I was in CWK today, and noticed that, even though I had the warrior boss and theif boss standing together with the archer boss, I was always hitting the archer boss when using Blast.

I've also noticed this when I was attacking HH in Evil Dead, making every hit of Power Stirke land on him, even with the Elderwraiths in my way. I would usually have to kill a couple Elders first before it would start to work, but after that it was perfect.

How does this little trick work? [/COLOR]

Either has to do with spawn time or which target you attacked first.