well, ticket price to get full attendance doesn't really same for everyone in same level,
even on my team, i need to set different price for each competition to get max attendance with 5% fans support as below
league - 14
Champion league - 20
Cup - 19
so, what you have to do is reducing your price ticket by 1 until you get 5% fans support
or upgrade your parking and utility
when you got full attendance, then try increase again your ticket price by 1 and see how it goes.