You could well be right on the heat transfer causing a bit of temperature lift, although compared with the data that Peter originally provided I think you're doing well. I would be happy with those numbers anyway.
As I said, I'm probably a week away from assembly and so things might change but this is where I'm at. The Airbox is finished, it's basically the OEM one with a new inlet and looks remarkably like yours
The filter has more surface area than the round one and the casing for that is still in the "scrappy" state while I tidy up the GRP. Today I have been learning how to make louvres in Al which I hope will both channel air into the filter and also cut down on water/spray ingress. That's what's been taking the time, trying to come up with a way to protect the paper filter from direct water splashes from underneath. I don't deliberately take the car out in the rain but in England it's a given that you'll get very wet at some point.
Dumb question time, how do you get your temperature and pressure measurements ? Is it specialist or DIY kit ? Pressure measurements is sounding high tech !