How to deal bonus damage correctly with sword?

I created a sword with 10 based damage and dealing 10%max health damage as a bonus. I set 10 as its damage to mob/animals and then use "deal 10%max health of target entity damage to target entity" block in "when entity is hit by tool". Finally I found it can only deal 10% max health damage without 10 based damage.

I have tried to change the contents of previous block to"deal 10+10%max health of target entity damage to target entity" . It does work. But its damage won't improve when it is enhanted. How to solve the problem?

Hoping my expression is exact enough to understand. I'm sorry for my poor English.