It’s both, but your head is a huge source of drag. The more you can get it in line with your back, the more aero you’ll be.
I know that’s why I said allow me to disregard the question
My Sarcasm Detector has been on the fritz…need to take it into the shop. 
I have both the Ventral and Ventral Air. Both are great helmets and you really can feel the air pulling through the Ventral, especially as you build speed.
The Ventral Air though is so comfortable. It became my go to helmet for XC MTB riding and I also wore it for Leadville. I would simply not notice it being on, it is that comfortable.
On the road I tend to lean towards the Ventral, but on really hot days I’ll go Ventral Air.
Somewhere I saw a quote from POC that the Ventral Air was just as aero as the Ventral up to a certain speed and then above that speed the Ventral had a slight advantage. I want to say 30mph, but I don’t remember exactly.
Great hijack. 
I bought one of these this week too. My first ride impression is very positive. It does “feel” faster, smoother and quieter than my previous Kask mojito.
This year I am going to throw extra effort at maximising aero gains to supplement my aging legs.
Triathlete here. I have the Aerohead and the P-09. I started with the Aerohead but my neck would get sore after around 2 hours, so I switched to the P-09, which is significantly lighter.
I don’t know which one is more aero on me, but I can add a few practical considerations for anyone trying to choose between these two helmets:
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P-09 is quite a bit lighter.
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Aerohead has a great magnetic visor system, and you can order a clear shield in addition to the tinted one that comes with it. It’s great for shorter distance events where I want to put the helmet on as quick as I can. Then I put the visor on after I’m on the bike.
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Aerohead has great visibility with the visor, both to the sides and looking forward, even when in full aero position.
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The “visor” on the P-09 is terrible, IMO. It isn’t large enough to block the wind, so it really dried my eyes out. I removed it and use my sunglasses instead. No such issues with the Aerohead visor.
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The Aerohead was comfortable right out of the box. The P09 didn’t fit the shape of my head. I used a Dremel to round out a few areas and not it fits fine. My wife also ordered a P09 and found it extremely uncomfortable because the internal shape didn’t match the shape of her forehead. So ended up returning it and sticking with her Advantage 2, which we bought for around $70 new last year.
Well I got the Aerohead. In all, I am really happy with the purchase. Price is good ($240 on eBay). I bought the white one hoping it will be a bit cooler in the summertime, although it definitely doesn’t look as good as the black ones. The ventilation is great, visibility is great, and subjectively, it does appear I am faster on my regular routes. Set a bunch of PRs while doing fitness/tempo rides (yeah, I’m the goon riding recreationally with his aero helmet, wah wah). I don’t have any reference for the weight of the helmet, but I felt that the helmet was plenty light out of the box. In all, I would recommend the Aerohead to anyone. I think Giro did a really good job. DW
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