The app puts the base pen for the shell at 175mm but the game lists it as 200mm.
I’m assuming the game is correct and the app is based on the test version stats?
I see the app uses 200mm as well. The effective piercing power shown in the app in the info panel on the left is dependent on the distance. The value of 200mm corresponds to 100m distance and 175mm corresponds to 500m distance. Could you check the pen power at 100m?