Cost to build t2 mex - 900 mass
Cost to upgrade t1 mex to t2 mex - 900 mass
Cost to build t2 radar - 180 mass
Cost to upgrade t1 radar to t2 radar - 180 mass
Cost to build t3 UEF shield - 3300 mass
Cost to upgrade t2 shield to t3 shield - 3300 mass
The "counterintuitive" aspect is adding a weird rule to t3 mex upgrades. The game is perfectly consistent. The only area the game doesn't work like this is support factories.