Mods, books and armor with the same effects should stack...

[Diragor]

I got myself the book that let's me heal on each hit and also the mod that does the same.. I though "Nice now I heal 2 hp per hit...But no it won't stack which is a real shame. Why not? Please change this

 

[BFT2020]

I got myself the book that let's me heal on each hit and also the mod that does the same.. I though "Nice now I heal 2 hp per hit...But no it won't stack which is a real shame. Why not? Please change this

I don't recall any mod item that adds HP per punch?  Which one are you referring to?

The book (bar brawler) does add 1 hp for each punch. 

The only mod item I know of that adds health is the Fortifying Grip which adds 1 hp every 5 seconds when the item is held and your HP is under 50%

And none of the armors give you hp recovery from hits that I could see