Thanks gents..
I had considered that a few feet back and to the side of the radiator duct the air would be sufficiently mixed to be relatively close to the ambient temp.
Mike.. I cant get the filter anywhere near that close to the underside of the radiator.. its sitting almost directly behind the upper lip at the back of the radiator ducting in a known hot spot on a Coupe as I moved the battery into the engine bay, blocking the path for an inlet of that type. It would also be feeding on air from the cooling system pipe directly underneath.
Noted re opening the back of the bonnet hump... that air is directly in the path of the radiator outlet, rather than to the side as a bonnet vent would be. Regardless, its a high pressure zone at the bottom of the windscreen, that would force air into the engine bay then out, either under the car or via the bonnet vents which is all positive.
I had already made up an insulated air box (aka OEM).. was thinking I could give plan A a go, easily revert to some sort of a scoop behind the radiator ducting if required and maintain the bonnet vents for cooling / engine bay air flow if one was not used as an intake.
The other benefit of the bonnet inlet was the slightly longer induction tube from the MAF to the throttle body, which improves the accuracy of the reading for the ECU. I cant get this extension of the inlet tube with the filter behind the radiator.
Option C...!! duct air in from the side of the bonnet.. aka Clubman style side draft intake.. !
Heading to a performance tuner in a few weeks... will get their 26c worth and update..