It's true that there is some adiabatic cooling of the air flowing over the top of the wing but the effect is pretty small. If you start with the wing loading of your Cardinal RG (about 16 lb/ft^2) and assume that half the lift is produced by the drop in pressure over the wing (not accurate but close enough for this estimation) you get something like 1/10 inHg of pressure drop. 1 inHg pressure change is equal to about 2°C of temperature change so you'd be looking as a few tenths of a degree Celsius, hardly enough to matter. In any case, I've seen ice accumulation on wings hundreds of times in conditions ranging from trace to the severe end of moderate and IME it always builds on the leading edges before accumulating anywhere else on the lifting surfaces. On the flip side, TAT (total air temp), which accounts for the adiabatic heating that accompanies the compression at the leading edges (and temperature probes) doesn't represent the surface temperature of the ice collecting surfaces on an aluminum skinned wing because the metal is such a good conductor of heat that there's very little temperature rise on the leading edges.