Proportionate To What?

A little over a year ago I noted that no one knows what's meant by "proportionate response" anymore. The term comes from Catholic Just War teaching and here's part of what I wrote then:
My sense is that when the term is tossed around, what people are thinking is that if Hamas fires a few rockets into Israel, Israel may only toss a few rockets back in response. But that's to set Just War teaching on its head, since it is simply re-introducing the law of the Talion the teaching is meant to replace. The question is: proportionate to what? The answer isn't proportionate to what your enemy did to you (an eye for an eye), but proportionate to your end -- repelling him from your border, preventing further attack, or what have you.
I could have added (but didn't because I considered it self-evident) that proportionality includes the idea that the good achieved will outweigh the harm done, as discussed briefly here. I'm a bit doubtful that various UN and other international types who speak about "proportion" are really interested in Just War teaching, but even so, quite a few people are criticizing the misuse of the term today. Notably and humorously, VDH, with Some Moderate Proposals, such as:
1) Request that 50% of Israel's air-to-ground missiles be duds to ensure greater proportionality.

2) Allow Hamas another 1,000 free rocket launches to see if they can catch up with the body count.

See also: Leashing the Dogs of War (National Interest) and a bunch of links connected by Andrew McCarthy, here.

Update: Forgot to link the Michael Totten piece that started this discussion. The one that starts with this remark from last summer:

If someone was sending rockets on my house where my daughters were sleeping at night, I would do everything to stop it, and I would expect Israelis to do the same thing.” – President-elect Barack Obama
Then: More in this conversation.
A discussion of proportion absent one of war aims is incomplete.

I reject the usual definition that "anticipated goods of waging war must be commensurate to its expected harms" because neither the benefits or costs of war are easily discernible at its outset. A definition that empirical cannot be of any practical use. As well if it means "use enough force to get the job done" it is but a truism.