It's a gray area. If you can go and get it without making your partner look like a fool, have a patient whistle, let him have a crack, and then take it. If you've got to use a global satellite tracker to phone in the call, let it go. There's a point (which I cannot give by steps or feet, it's just a feel) at which I won't extend my boundaries on calls like this.
On the other hand, if you are looking and concentrating on your own area, you'll never see this...
