Do you know this situation: You have a corner-shelf in your shower and evertime you put your shampoo back, or touch the shelf (softly) the whole stuff falls down (and on your feet...)?
This is because the distance of the metal bars is much too wide...

You can use this support to ensure more flat surface for your items.

you can scale it with your 3D printing software to fit the size of your shelf. Even the thickness is editable. 3-5mm should be perfectly fine.