Filament Rack Shelf Insert

I've got this wall mounted filament storage rack that is cheap and works really well, but I kinda also want to store boxed filament on it. Boxes fit, but not well. This simple shelf fits over the spool bars to make the boxes sit nicely without risk of slipping and ending up corner down. This is the rack: https://www.amazon.com/dp/B0DC69S1TX