increased exceptional item chance not working as expected

1. Title: increased exceptional item chance not working as expected
2. Reproduction Rate: 100%
3. Blocker? no
4. Details: Both "artisan smithing hammer" and "smithing hammer of prosperity" give me an identical exceptional item chance, even though according to their descriptions, the prosperity tool should always have an exceptional item chance 2% higher.
5. Steps to Reproduce:
   - Try to craft an item with artisan smithing hammer equipped, note exceptional item chance
   - switch equipped tool to smithing hammer of prosperity, compare exceptional item chance
   
6. User Specs: irrelevant

My specific test:
I have 60 blacksmithing proficiency (lvl 72).
I am trying to craft a pair of epic plate boots.

expert blacksmithing table:
both artisan smithing hammer and smithing hammer of prosperity: 23% exceptional item chance
regular blacksmithing table:
both artisan smithing hammer and smithing hammer of prosperity: 22% exceptional item chance