Approx 1/8" is sufficient.
Hat is onto the reason. Constant pressure ? Isobaric? baloney actually not needed for Epsons.
You need to convert to a drop tube system to run pigment reliably. Use normal containers and have the tubes hang and drop into the ink bottles. Heavier pigmented/darker colors will usually have more sediments. This is always an issue with pigment. Epson uses steel balls in their carts that used to move and Canon uses flappers to stir things up.
Empty the tanks. Pull off the tubes. Seal the bottom up or use old bottles and drill holes into the caps.View attachment 101View attachment 103View attachment 102