General Tile Discussion

First time using a Tile Redi shower pan. The drain is a regular one not a trench. Planning to use 3x12” tiles on walls set horizontal. Based on the Tile Redi design drawings I thought the slope to the drain would start at each wall so there would be a straight edge to set the bottom row of tiles on. But now that the pan arrived I see that the slopes create a triangle shaped gap as the floor angles down. Two walls are going to be floor to ceiling tiles. The third wall will going to be floor to ceiling in the shower and then transition one row of tile to act as a baseboard. I would prefer this “baseboard” row would continue around the room at its full 3” height. So that creates a problem, trianglular slivers of tile filling the gap between the first row and the downward sloping pan floor. Is there a better solution to this?