I'm not sure if my cannon turrets simply aren't shooting over walls at all, or if they're leading the target so far ahead that they're essentially shooting at themselves, but they're doing way more damage to me than to the enemies... (75mm turrets with explosive uranium shells)

It is vanilla behaviour that cannon shells will collide with ANYTHING, whether friend or foe.

The parent mod "Schall Tank Platoon" already provided the choice to change such behaviour.
You should look for changing "force condition", which is under mod settings.
For example, the entry "Force condition Cannon shells", the vanilla (unchanged) default is "All". Changing it to either "Not same" or "Not friend" will make them not colliding with your own entities, like firing over walls or buildings, yet still hitting the enemies.