Scoops are making use of moving air, and the kinetic energy that it has as some speed... Hood scoops don't do a thing when you launch, because, well, nothing's moving yet. When you're screaming down the track at 100 +, that's a different story.
You are correct that at different elevations the atmospheric pressure changes, the higher you go up, the lower the pressure, and the worse your car, or you, will run. Gravity makes no difference on the air filter. I could hand you two 100 cubic foot CO2 tanks for a welder, one full and one empty, and I'll gauruntee that you can't tell me which is which without an accurate scale.
Cones have the advantage of more surface area, and the flow might look a little better because the air is coming in from all sides. I doubt you'd be able to see any difference just from that alone, again, go back to our previous disscussion about the restrictions and bends in the pipe.
Think about the obvious example: Does a vaccum sweeper run any better when you hold the nozzel straight up or down or any other direction, other than kinking the hose? Of course not. Same thing here. Our vaccum pumps have cylinders, not a centrifugal fan, but the result is the same.