I do pretty much the same thing.

In the IS Boxer Toolkit, I create an Action Target Group.
And add everyone to the group who will be healing.
In some character sets, toons are added to or removed from ATG's based on their spec or their stance/druid form... so sometimes the heal will be broadcast to their toon and other times not, depending on if they're a member of whatever ATG.

I always choose the target ATG from the drop down.
And choose block local click (kvm mode) too.
And then create the region, position it, sync it, and then save it as "auto".

Even if the local click is blocked, it broadcasts to all members of that group.
Which means your current toon gets the click when they're a member of the ATG.
But does not get the click if they're not a member of that ATG.