I'd rather see its rear armor being vulnerable then front one being stripped to medium tank level.
This thing was more durable then Tiger I and right not its a slower, stock KV-1.
The only unit that would benefit would be the Panzer IV and Pumas as the rear is 180 so any real AT will still penetrate if the Churchill decides to face its rear towards the enemy. Even Shreks will go through the majority of the time when firing at max range(160 pen).
Even then and now flanking makes no difference towards engaging a Churchill aside from blocking due to its enormous health pool which is its greatest strength whereas a KV-1 relies far more on armour due to its 800 hp where if it is flanked, it'll die much faster. It only takes 1 more shot to kill over a medium tank unlike the Churchill.
If it really needs the armour, as I said, make it around the 240-260 mark.