The front of the trigger is a good place to start inasmuch as it is related to the position of at least one hand that will be sensing the balance. Hinge pins don't care where your hands are. That said, most field or neutral guns will balance about 4.5" forward of the trigger. Target guns are usually built with a weight-forward bias, and that might equate to about 4.75" to 5.5" in front of the trigger. That latter length, 5.5", starts to feel a bit unwieldy.
The Iver balances at 6.5 inches from the front trigger, which is just after where the side of the forearm becomes parallel to the barrel:
