Considering the physical location & secondary vibrational forces from engine, securing the CPS from the underside is probably a better fastening method that from topside. Difficulty in removing it probably more akin to exposure to heat, similar to removing an oxygen sensor. CPS was probably mounted to engine prior to engine being dropped into car & only the pigtail had to be connected. Might be a good practice to use an anti-seize paste on the screw threads, especially since part is probably a recurring failure over time. I could be convinced to just replace the CPS every 4-5 years, depending on mileage incurred during ownership.

My $0.02.