If you stab a spear at point blank it glances, even if they're moving forward. That shouldn't happen. So unless they're willing to remove the minimum range on the stab so long as the head isn't already past them, then no.
Realistically, if you have a spear planted firmly against someones chest and they start to move forward, what'll happen? Right, they impale themselves like an idiot. If the person isn't even wearing a shirt, it'll hardly take anything to penetrate realistically. I can't tell you how many times I've had my spear bounce off of naked flesh because I didn't bother to wiggle my attack against a fleeing peasant/archer.