What would a "proportionate response" look like?

A single Israeli air strike is going to kill at least as many people as Hamas can kill in twelve months. Does that mean Israel should be given a “license” of one air strike per year to use in the war? If IDF commanders want to take out a target where they expect five Hamas leaders or fighters to be killed, do they have to wait until five Israelis are killed first? If the Israelis endure rocket fire until one civilian is killed, do they get a “kill one Palestinian terrorist” coupon?

One problem here is that it’s not at all clear how they think Israelis should go about doing it.