The tau V8 has an upper and lower oil pan sections and when the Genesis is on ramps the oil cannot all drain out of the upper section of the oil pan, which is toward the rear of the car. You may be thinking that the lower part where the drain plug is located is the complete pan, however the rest of the pan is above and to the rear, hence the reason for the car needing to be level. If you look closely at the photo below you can see the upper oil pan section (silver) along the bottom of the block with the small lower (black) section attached to it.
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schematic
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Interesting on upper and lower pan...you could drain it on stands, empty what's in the lower part, lower the car back on wheels (with plug back in) to let oil from upper flow to lower then jack back up to get the rest