People think we know well their TP, think we can rely on what their are doing to see their TP Issues, the only way for us to know their TP is based on our own and it's not really an exact science, that is why most of time a ninja goad... another ninja, it's a way to told them "hey i'm running out of tp so do you, i give you goad, give me yours !" and it work perfectly, nearly all the time.
i usually use it on war too when he's doing big pull, or on a recently raised target.

other than that, if you dont ask, you dont get, unless i'm running myself out of tp or we set it before the run.