We've done quite a bit of testing and found the most accurate place for an OAT probe is on the wing. A few ribs outboard is a good place (all the way out is fine too). The most inaccurate place is the naca vent on the fuselage. Just my .02.
On my RV8 it is inboard on right wing. I am going to have to place the one for the RV10 in the next few weeks. I will probably put it in the same place.
I have two and both were in the NACA air inlet and reading the same. I moved one of them to under the wing in the root fairing area and the reading is exactly the same as before. A few test that I have run, indicated accurate reading and they are certainly accurate on the ground as it is easy to test.
Hope this helps.
One in each rear NACA for each of the dual Dynons and one in the wing root for the MVP-50 engine monitor. Have not flown the 10 but I have the same set up in the 8 one in the NACA and one in the wing root.
They are both within a couple of degrees.