Crafting Abyss Gears

I have 3 insight III crit rating Lv3 Abyss Gears but the Witch won't let me create a L4. I don't understand.

I have other Abyss Gears both L3, two attack 3 Abyss Gears but she won't let me synth those two together for one L4, I don't understand.

I thought the system was as long as you have two of the same, you can keep leveling up the Abyss Gear, or are the Gears capped at 3?