Shortie RR to AI explanation

I'm not sure if I have this right. I'm thinking of when someone raises and a short stack goes all in but the amount he reraises is less than a full BB (and he is last to act). I'm guessing the logic is that the EP raiser would have had to make his raise bigger in the first place so he doesn't get the right to RR again after Shortie comes AI? Do I have this right?

If I raise to $3 in EP in a .50/1 game, then there is a caller, then a shorty reraises AI to $4, I cannot 4bet. If someone who acts after the shortstack wants to 4bet, they can

Now, if the shortstack reraises to $5 or more, the action is reopened and I can then 4bet if I wish.