SKETCH Advancement

I'm thinking about advancement for SKETCH. The core rules don't has any, it is built for 'one off' games. That and the math won't take much tinkering,

'Or Lower'
6 --- 100%
5 --- 83%
4 --- 66%
3 --- 50%
2 --- 33%
1 --- 16%

In SKETCH Horror, 'advancement' is handled by Gifts, non-assumed gear, and Fate Points. which buy re-rolls or add to damage.

Highway from Hell uses a broader point system, I was thinking of advancing specific skills within an attribute.

Say, from Ana's attribute at 3

Hurting Stuff:
Hurting Stuff with Your Bare Hands
Stabbing, Slashing and Bludgeoning
Shooting Stuff

she takes 'Hurting Stuff with a Tire Iron' at 4. Any other combat skill is still 3.

Or I could Gift her with a +1 tire iron.