Perspective with unique view preference for subtasks?

The hierarchy is Project > Task > Subtask, right? By Subtask I mean what I get when I indent a task, at which point it has a parent task.
I would like to set up a perspective that shows available Tasks and all Subtasks of available Tasks. Not possible, right?

All
Not a project or group
Available

None
Has a due date

Presentation:
Group and sort: All projects
Group actions by: …
Sort actions by: Projects Order

if I get you right.

That doesn’t do what I was asking for. I tried a few variations of it as well.

I think what would work is if the rule pull-down list included “Is a subtask”.

Part of the problem here is that a task that has unfinished subtasks is never considered “Available”; it’s considered blocked by the subtasks until they are completed.