So long as the cone is in the original place as the airbox and not on the turbo itself, there is less than 2C difference between ambient and air filter temp.
I USE NO HEAT SHEILD BETWEEN TURBO AND AIR FILTER.
IT ABSOLUTELY DOES NOT DRAW ANY AMOUNT OF HOT AIR.
I have sensors all over my car(sapphy) and even zeroed the sensors so they read precisely the same before using, I have a sensor mounted in the end rubber bit of the group a cone filter, you pick up a bit of heat around town speeds, up to 15C on a really hot day, but once above 30mph it settles back down within 500 metres to within 2C of ambient.
I also had sensors in the pipe between turbo intercooler, and intercooler plenum and plenum itself, now just run temp sensor in air filter end(so it goets no cooling air flow, just static air), and plenum, all in about £6-£8 cost for a switchable 2 temp digital readout, same ones on ebay for around £40, which are only 1 temp reading!!
tabetha