Minecraft v1.14.4
Forge v28.1.90
Cosmetic Armor v1a

If I click on the Green Book for the Crafting Preview in the Cosmetic Armor inventory, the JEI Favorites List overlaps it. This doesn't happen in the normal player inventory.

Thank you for your report.
Sorry, I am not going to fix this.
Even though I included the crafting grid and the guide book, I don't think a small 2x2 crafting grid will be used in a complex crafting.
They are there just for some simple on-the-go crafting you happen to remember before putting your cosmetic items in your cosmetic slots.

Fair enough.