Bitter taste of defeat! So much coolant in the oil pan.

I'm absolutely not trying to be a smart-*** here, just a person with very limited experience (but not a total idiot) trying to understand what is happening and why. I have been trying to build a complete picture of what the water passages inside the engine actually look like and haven't been able to find much in my books or on the internet.

According to my manual, the 19" radiator+water jacket+hoses total capacity = 16 quarts (4 gallons).

I don't know what the actual radiator's capacity is. But I'm going to assume that the water level in the radiator is going to be the same height as right below wherever it is leaking into the block or oil pan.

I don't know the capacity of the water jacket in the block. Is it significant?

So adding a gallon of water to a radiator (cannot see the water level in it so that means it is at least somewhat lower than the top) and then seeing it come out of the oil pan soon afterward suggests to me that the whole system is not filling up all the way to the top of the heads, to where it could leak out of the intake manifold gasket.

I say this because there is no way that 3 gallons of coolant/water came out after I'd watched the water I poured in come out the oil pan hole, when I pulled the lower hose between the radiator and water pump.

Am I missing something obvious?