Well I got a users manual for it in email today.

The Arc Force knob is for stick welding and not Tig,which is why it does nothing in TIG mode.

Aparently you can adjust the penetration rate without increasing the amps. According to the book, it works similar to pulling the rod away and back into the weld pool. By pulling away you lessen the penetration without changing amps and pushing in will increase penetration at the same amps.
This knob allows you turn this up and down. At 1, changing the arc distance wont change the penetration. At 10 it is very sensitive to arc distance.

Pretty advanced option for stick welding. Never seen a stick welder with that as an option before. The manual says thats its really good for vertical and overhead welding, for changing direction eaisly, root welds and fillets.

Mystery solved.

Now just to teach myself TIG welding