It is a combination of how tall the front is, and if it sweeps backwards a bit, or is practically perpendicular to the ground.

What matters is how likely a pedestrian is to be pulled under the vehicle, instead of pushed up onto the hood. You can have a fairly tall grill, if it is angled backwards somewhat. And it won’t be a near instant death bulldozer for pedestrians.
Tall and flat is the most dangerous combination, and that is exactly the trend of most big and giant trucks & SUVs.