Dry sump oil level

I'm almost done retuning my yz426 back to a dry sump from a wet sump block off kit which the bike came with. Now that I fully understand the path the oil takes and how the return and feed pump work, I find myself wondering why the level in the frame needs to be so low on the dipstick. Basically if the bike holds around 1.5 quarts, how come you can't add an extra 1/2 quart to get more total volume. The level in the frame would rise, but the oil feed line comes from the bottom of the frame anyways. If its weight, it doesn't matter to me. The only other possible issue I could think of would be that maybe an over filled frame might create back pressure on the return line. Am I missing anything and what's the theory behind not filling the frame higher.

There is a vent line on the left hand side of the oil tank that runs to the valve cover and if the tank is over filled it runs down the line into the valve cover and gets blown out of the breather.

As long as the oil level in the tank never rises beyond the pressure balance vent that runs back to the engine, you can put as much in it as you want. You need a minimum of about 2" of air over the oil.

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