My uncle bought a $400 flir camera for the same reason and it ended up being a $6 wire nut in the attic. At least now you own a cool toy for checking if the walls are cold.

Eggshells are more of a calcium thing than a magic trick, and most soil already has plenty, so they probably weren't the reason your numbers jumped. The new spot with all that sun and moving them around is what really did it.

Checking every 10 feet is just normal line work, not some Tucson secret.