A tray dimension describes the outside of a shower. The space you can move in also depends on how far the storage and fittings project into it. In our Aberdeen room, a single large glass panel defines the walk-in shower and two deep recesses give products a home beside the fittings. The walls can hold the bottles while the tray stays available for washing.
For a similar design, draw the usable interior with the fittings and any shelves shown at their real depth. Mark the position where you stand and check whether bottles can be reached comfortably from there. Then compare a recessed shelf with a projecting shelf and see how each changes the space for turning. This makes the benefit of a recess easier to judge against the depth it needs in the wall. It also helps you choose a glass position that complements the space left for movement.
