Tub walls and pony walls
When you have a your tub and shower laid out next to each other the dividing wall and/or ledge should be hot mopped. That wall needs to be faced with sheathing or filled between the studs from bottom plate to top with solid material. If the tub is lower than the top of the dividing wall then the portion facing the tub should be blocked and can be mopped down to the tub deck.