like stated i believe the factory computer reads, air filter air temp, and intake manifold air temp, so IAT2 (intake air temp 2) should be intake manifold, should tell you how effiecient the intercooler is, IAT will tell you what kind of air the engine is taking in, some may note that an aftermarket intake will draw in warmer air then a stock intake.
NOW moving on to post turbo, you would honestly probably be better off mounting a EGT probe post turbo, there is a formula for turbo outlet temperatures, but basically it boils down to 10psi of boost equals 100 degrees increased air temp over ambient, so if your making 25 psi, temps are probably 300+ degrees, a regular temp sensor wont read that, I have thought about puting the egr inlet temp sensor in my outlet pipe to see what the temps are like.