Generally speaking. the height of the spark plugs or the crank position sensor on the engine is usually the lowest point where engine would stop when water floods that zone.
Diesel sengine will not be affected all the way up to the snorkel of the air filter.
Speaking of air filter... that is the another issue where the splash is enough to cause engine engine to sieze. So it is important to drive slow through flooded street.
It is important to wash the undercarriage soon after you pass the flooded street to remove any contaminants.
So how high realistically? I would have to say the center of the wheel/tire should be the highest for safety reason. Best case is not to do it as you don't really know how deep the water is.